billboards!

CMakeLists.txt

@@ -106,10 +106,12 @@ set(TWN_NONOPT_SOURCE_FILES
         src/twn_textures.c src/twn_textures_c.h
 
         src/rendering/twn_draw.c src/rendering/twn_draw_c.h
+        src/rendering/twn_quads.c
         src/rendering/twn_sprites.c
         src/rendering/twn_rects.c
         src/rendering/twn_text.c
         src/rendering/twn_triangles.c
+        src/rendering/twn_billboards.c
         src/rendering/twn_circles.c
         src/rendering/twn_skybox.c
         src/rendering/twn_fog.c)

apps/demos/scenery/scenes/ingame.c

@@ -158,6 +158,8 @@ static void draw_terrain(SceneIngame *scn) {
                             (Vec2){ 128, 0 },
                             (Vec2){ 0, 0 },
                             (Vec2){ 0, 128 });
+
+            draw_billboard("/assets/grasses/10.png", (Vec3){ (float)x, d1 + 0.1f, (float)y }, (Vec2){0.3f, 0.3f}, (Color){255, 255, 255, 255}, true);
         }
     }
 }
@@ -200,7 +202,7 @@ static void ingame_tick(State *state) {
     generate_terrain(scn);
     draw_terrain(scn);
 
-    draw_skybox("/assets/miramar/miramar_*.tga");
+    // draw_skybox("/assets/miramar/miramar_*.tga");
     draw_fog(0.9f, 1.0f, 0.05f, (Color){ 140, 147, 160, 255 });
 }
 

include/twn_draw.h

@@ -54,6 +54,7 @@ TWN_API void draw_triangle(char const *texture,
 
 // TODO: decide whether it's needed to begin with?
 //       intended usage for it is baked lighting, i would think.
+// TODO: instead add optional color parameters to 'draw_triangle'
 /* pushes a colored textured 3d triangle onto the render queue */
 // void unfurl_colored_triangle(const char *path,
 //                              Vec3 v0,
@@ -66,7 +67,7 @@ TWN_API void draw_triangle(char const *texture,
 //                              Color c1,
 //                              Color c2);
 
-TWN_API void draw_billboard(const char *path,
+TWN_API void draw_billboard(const char *texture,
                             Vec3 position,
                             Vec2 size,
                             Color color,        /* optional, default: all 255 */

include/twn_vec.h

@@ -9,6 +9,26 @@
 #include <math.h>
 
 
+static inline Vec2 vec2_add(Vec2 a, Vec2 b) {
+    return (Vec2) { a.x + b.x, a.y + b.y };
+}
+
+static inline Vec2 vec2_sub(Vec2 a, Vec2 b) {
+    return (Vec2) { a.x - b.x, a.y - b.y };
+}
+
+static inline Vec2 vec2_div(Vec2 a, Vec2 b) {
+    return (Vec2) { a.x / b.x, a.y / b.y };
+}
+
+static inline Vec2 vec2_mul(Vec2 a, Vec2 b) {
+    return (Vec2) { a.x * b.x, a.y * b.y };
+}
+
+static inline Vec2 vec2_scale(Vec2 a, float s) {
+    return (Vec2) { a.x * s, a.y * s };
+}
+
 static inline Vec3 vec3_add(Vec3 a, Vec3 b) {
     return (Vec3) { a.x + b.x, a.y + b.y, a.z + b.z };
 }
@@ -17,12 +37,12 @@ static inline Vec3 vec3_sub(Vec3 a, Vec3 b) {
     return (Vec3) { a.x - b.x, a.y - b.y, a.z - b.z };
 }
 
-static inline Vec2 vec2_div(Vec2 a, Vec2 b) {
-    return (Vec2) { a.x / b.x, a.y / b.y };
+static inline Vec3 vec3_div(Vec3 a, Vec3 b) {
+    return (Vec3) { a.x / b.x, a.y / b.y, a.z / b.z };
 }
 
-static inline Vec2 vec2_scale(Vec2 a, float s) {
-    return (Vec2) { a.x * s, a.y * s };
+static inline Vec3 vec3_mul(Vec3 a, Vec3 b) {
+    return (Vec3) { a.x * b.x, a.y * b.y, a.z * b.z };
 }
 
 static inline Vec3 vec3_scale(Vec3 a, float s) {
@@ -83,15 +103,23 @@ static inline Vec3 vec3_rotate(Vec3 v, float angle, Vec3 axis) {
                                 )(p_any_vec2))
 
 #define m_vec_add(p_any_vec0, p_any_vec1) (_Generic((p_any_vec0),   \
+                                    Vec2:   vec2_add,               \
                                     Vec3:   vec3_add                \
                                 )(p_any_vec0, p_any_vec1))
 
 #define m_vec_sub(p_any_vec0, p_any_vec1) (_Generic((p_any_vec0),   \
+                                    Vec2:   vec2_sub,               \
                                     Vec3:   vec3_sub                \
                                 )(p_any_vec0, p_any_vec1))
 
 #define m_vec_div(p_any_vec0, p_any_vec1) (_Generic((p_any_vec0),   \
-                                    Vec2:   vec2_div                \
+                                    Vec2:   vec2_div,               \
+                                    Vec3:   vec3_div                \
+                                )(p_any_vec0, p_any_vec1))
+
+#define m_vec_mul(p_any_vec0, p_any_vec1) (_Generic((p_any_vec0),   \
+                                    Vec2:   vec2_mul,               \
+                                    Vec3:   vec3_mul                \
                                 )(p_any_vec0, p_any_vec1))
 
 #define m_vec_scale(p_any_vec, p_any_scalar) (_Generic((p_any_vec),    \

src/rendering/twn_billboards.c

@@ -0,0 +1,168 @@
+#include "twn_draw.h"
+#include "twn_draw_c.h"
+#include "twn_engine_context_c.h"
+#include "twn_textures_c.h"
+#include "twn_types.h"
+#include "twn_vec.h"
+
+#include <stb_ds.h>
+
+
+void draw_billboard(const char *texture,
+                    Vec3 position,
+                    Vec2 size,
+                    Color color,
+                    bool cylindrical)
+{
+    // TODO: order drawing by atlas id as well, so that texture rebinding is not as common
+    const TextureKey texture_key = textures_get_key(&ctx.texture_cache, texture);
+
+    struct MeshBatchItem *batch_p = hmgetp_null(ctx.billboard_batches, texture_key);
+    if (!batch_p) {
+        struct MeshBatch item = {0};
+        hmput(ctx.billboard_batches, texture_key, item);
+        batch_p = &ctx.billboard_batches[hmlenu(ctx.billboard_batches) - 1]; /* TODO: can last index be used? */
+    }
+
+    struct SpaceBillboard billboard = {
+        .color = color,
+        .cylindrical = cylindrical,
+        .position = position,
+        .size = size,
+    };
+
+    struct SpaceBillboard *billboards = (struct SpaceBillboard *)(void *)batch_p->value.primitives;
+
+    arrpush(billboards, billboard);
+    batch_p->value.primitives = (uint8_t *)billboards;
+}
+
+
+/* reused for all billboards */
+static Vec3 right_plus_up;
+static Vec3 right_minus_up;
+static Vec3 right_plus_up_cylindrical;
+static Vec3 right_minus_up_cylindrical;
+
+/* precalculate (right + up) and (right - up) that are used with all batches */
+static void calculate_intermediates(void) {
+    Vec3 const right = { camera_look_at_matrix.row[0].x, camera_look_at_matrix.row[1].x, camera_look_at_matrix.row[2].x };
+    Vec3 const up = { camera_look_at_matrix.row[0].y, camera_look_at_matrix.row[1].y, camera_look_at_matrix.row[2].y };
+
+    right_plus_up = m_vec_add(right, up);
+    right_minus_up = m_vec_sub(right, up);
+
+    Vec3 const up_cylindrical = { 0, 1, 0 };
+
+    right_plus_up_cylindrical = m_vec_add(right, up_cylindrical);
+    right_minus_up_cylindrical = m_vec_sub(right, up_cylindrical);
+}
+
+
+/* http://www.lighthouse3d.com/opengl/billboarding/index.php?billCheat2 */
+void finally_draw_billboard_batch(struct MeshBatch const *batch,
+                                  TextureKey texture_key)
+{
+    const size_t primitives_len = arrlenu(batch->primitives);
+
+    /* nothing to do */
+    if (primitives_len == 0)
+        return;
+
+    /* TODO: only do it once per frame */
+    calculate_intermediates();
+
+    const Rect srcrect = textures_get_srcrect(&ctx.texture_cache, texture_key);
+    const Rect dims    = textures_get_dims(&ctx.texture_cache, texture_key);
+
+    const float wr = srcrect.w / dims.w;
+    const float hr = srcrect.h / dims.h;
+    const float xr = srcrect.x / dims.w;
+    const float yr = srcrect.y / dims.h;
+
+    const Vec2 uv0 = { xr + 1 * wr, yr + 0 * hr };
+    const Vec2 uv1 = { xr + 1 * wr, yr + 1 * hr };
+    const Vec2 uv2 = { xr + 0 * wr, yr + 1 * hr };
+    const Vec2 uv3 = { xr + 0 * wr, yr + 0 * hr };
+
+    /* emit vertex data */
+    VertexBuffer const buffer = get_scratch_vertex_array();
+    VertexBufferBuilder builder = build_vertex_buffer(buffer, sizeof (ElementIndexedBillboard) * primitives_len);
+
+    for (size_t i = 0; i < primitives_len; ++i) {
+        struct SpaceBillboard const billboard = ((SpaceBillboard *)(void *)batch->primitives)[i];
+
+        /* a = (right + up) * size, b = (right - up) * size*/
+        Vec3 a, b;
+        if (billboard.cylindrical) {
+            a = vec3_mul(right_plus_up_cylindrical, ((Vec3){billboard.size.x, billboard.size.y, billboard.size.x}));
+            b = vec3_mul(right_minus_up_cylindrical, ((Vec3){billboard.size.x, billboard.size.y, billboard.size.x}));
+        } else {
+            a = vec3_mul(right_plus_up, ((Vec3){billboard.size.x, billboard.size.y, billboard.size.x}));
+            b = vec3_mul(right_minus_up, ((Vec3){billboard.size.x, billboard.size.y, billboard.size.x}));
+        }
+
+        struct ElementIndexedBillboard const payload = {
+            /* TODO: use the flat shading to not set two of the colors */
+            .c0 = billboard.color,
+            .c1 = billboard.color,
+            .c2 = billboard.color,
+            .c3 = billboard.color,
+
+            .uv0 = uv0,
+            .uv1 = uv1,
+            .uv2 = uv2,
+            .uv3 = uv3,
+
+            .v0 = vec3_sub(billboard.position, b),
+            .v1 = vec3_sub(billboard.position, a),
+            .v2 = vec3_add(billboard.position, b),
+            .v3 = vec3_add(billboard.position, a),
+        };
+
+        push_to_vertex_buffer_builder(&builder, &payload, sizeof (payload));
+    }
+
+    /* commit to drawing */
+    DeferredCommandDraw command = {0};
+
+    command.vertices = (AttributeArrayPointer) {
+        .arity = 3,
+        .type = GL_FLOAT,
+        .stride = offsetof(ElementIndexedBillboard, v1),
+        .offset = offsetof(ElementIndexedBillboard, v0),
+        .buffer = buffer
+    };
+
+    command.texcoords = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = offsetof(ElementIndexedBillboard, v1),
+        .offset = offsetof(ElementIndexedBillboard, uv0),
+        .buffer = buffer
+    };
+
+    command.colors = (AttributeArrayPointer) {
+        .arity = 4,
+        .type = GL_UNSIGNED_BYTE,
+        .stride = offsetof(ElementIndexedBillboard, v1),
+        .offset = offsetof(ElementIndexedBillboard, c0),
+        .buffer = buffer
+    };
+
+    command.textured = true;
+    command.texture_key = texture_key;
+
+    command.element_buffer = get_quad_element_buffer();
+    command.element_count = 6 * (GLsizei)primitives_len;
+    command.range_end = 6 * (GLsizei)primitives_len;
+
+    use_texture_mode(textures_get_mode(&ctx.texture_cache, texture_key));
+
+    DeferredCommand final_command = {
+        .type = DEFERRED_COMMAND_TYPE_DRAW,
+        .draw = command
+    };
+
+    arrpush(deferred_commands, final_command);
+}

src/rendering/twn_circles.c

@@ -1,6 +1,7 @@
 #include "twn_engine_context_c.h"
 #include "twn_draw_c.h"
 #include "twn_draw.h"
+#include "twn_util_c.h"
 
 #include <SDL2/SDL.h>
 #include <stb_ds.h>
@@ -66,3 +67,57 @@ void create_circle_geometry(Vec2 position,
         vertices[num_vertices - 1].y += position.y;
     }
 }
+
+
+void render_circle(const CirclePrimitive *circle) {
+    static Vec2 vertices[CIRCLE_VERTICES_MAX];
+    static int prev_num_vertices = 0;
+    static Vec2 prev_position = {0};
+
+    int const num_vertices = MIN((int)circle->radius, CIRCLE_VERTICES_MAX);
+
+    if (prev_num_vertices != num_vertices) {
+        create_circle_geometry(circle->position,
+                               circle->radius,
+                               num_vertices,
+                               vertices);
+        prev_num_vertices = num_vertices;
+        prev_position = circle->position;
+    } else {
+        /* reuse the data, but offset it by difference with previously generated position */
+        /* no evil cos sin ops this way, if radius is shared in sequential calls */
+        Vec2 const d = { prev_position.x - circle->position.x, prev_position.y - circle->position.y };
+        for (int i = 0; i < num_vertices; ++i)
+            vertices[i] = (Vec2){ vertices[i].x - d.x, vertices[i].y - d.y };
+        prev_position = circle->position;
+    }
+
+    VertexBuffer buffer = get_scratch_vertex_array();
+    specify_vertex_buffer(buffer, vertices, sizeof (Vec2) * num_vertices);
+
+    DeferredCommandDraw command = {0};
+
+    command.vertices = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = sizeof (Vec2),
+        .offset = 0,
+        .buffer = buffer
+    };
+
+    command.constant_colored = true;
+    command.color = circle->color;
+
+    command.element_buffer = get_circle_element_buffer();
+    command.element_count = (num_vertices - 2) * 3;
+    command.range_end = (num_vertices - 2) * 3;
+
+    use_texture_mode(circle->color.a == 255 ? TEXTURE_MODE_OPAQUE : TEXTURE_MODE_GHOSTLY);
+
+    DeferredCommand final_command = {
+        .type = DEFERRED_COMMAND_TYPE_DRAW,
+        .draw = command
+    };
+
+    arrpush(deferred_commands, final_command);
+}

src/rendering/twn_draw.c

@@ -29,8 +29,12 @@ void render_queue_clear(void) {
     /* and start overwriting the existing data */
     arrsetlen(ctx.render_queue_2d, 0);
 
+    /* TODO: free memory if it isn't used for a while */
     for (size_t i = 0; i < hmlenu(ctx.uncolored_mesh_batches); ++i)
         arrsetlen(ctx.uncolored_mesh_batches[i].value.primitives, 0);
+
+    for (size_t i = 0; i < hmlenu(ctx.billboard_batches); ++i)
+        arrsetlen(ctx.billboard_batches[i].value.primitives, 0);
 }
 
 
@@ -332,18 +336,23 @@ static void render_2d(void) {
 static void render_space(void) {
     /* nothing to do, abort */
     /* as space pipeline isn't used we can have fewer changes and initialization costs */
-    if (hmlenu(ctx.uncolored_mesh_batches) == 0)
-        return;
+    if (hmlenu(ctx.uncolored_mesh_batches) != 0 || hmlenu(ctx.billboard_batches) != 0) {
+        use_space_pipeline();
+        apply_fog();
 
-    use_space_pipeline();
-    apply_fog();
+        for (size_t i = 0; i < hmlenu(ctx.uncolored_mesh_batches); ++i) {
+            finally_draw_uncolored_space_traingle_batch(&ctx.uncolored_mesh_batches[i].value,
+                                                        ctx.uncolored_mesh_batches[i].key);
+        }
 
-    for (size_t i = 0; i < hmlenu(ctx.uncolored_mesh_batches); ++i) {
-        draw_uncolored_space_traingle_batch(&ctx.uncolored_mesh_batches[i].value,
-                                            ctx.uncolored_mesh_batches[i].key);
+        for (size_t i = 0; i < hmlenu(ctx.billboard_batches); ++i) {
+            finally_draw_billboard_batch(&ctx.billboard_batches[i].value, ctx.billboard_batches[i].key);
+        }
+
+        pop_fog();
     }
 
-    pop_fog();
+    render_skybox(); /* after everything else, as to use depth buffer for early z rejection */
 }
 
 
@@ -357,7 +366,6 @@ void render(void) {
 
     start_render_frame(); {
         render_space();
-        render_skybox(); /* after space, as to use depth buffer for early z rejection */
         render_2d();
     } end_render_frame();
 }
@@ -370,6 +378,7 @@ void draw_camera(Vec3 position, float fov, Vec3 up, Vec3 direction) {
         .target = direction,
         .up = up,
     };
+
     camera_projection_matrix = camera_perspective(&camera);
     camera_look_at_matrix    = camera_look_at(&camera);
 }
@@ -378,9 +387,11 @@ void draw_camera(Vec3 position, float fov, Vec3 up, Vec3 direction) {
 /* TODO: https://stackoverflow.com/questions/62493770/how-to-add-roll-in-camera-class */
 DrawCameraFromPrincipalAxesResult draw_camera_from_principal_axes(Vec3 position, float fov, float roll, float pitch, float yaw) {
     (void)roll;
+
     float yawc, yaws, pitchc, pitchs;
     sincosf(yaw, &yaws, &yawc);
     sincosf(pitch, &pitchs, &pitchc);
+
     Camera const camera = {
         .fov = fov,
         .pos = position,
@@ -391,6 +402,7 @@ DrawCameraFromPrincipalAxesResult draw_camera_from_principal_axes(Vec3 position,
         })),
         .up = (Vec3){0, 1, 0},
     };
+
     camera_projection_matrix = camera_perspective(&camera);
     camera_look_at_matrix    = camera_look_at(&camera);
 
@@ -520,364 +532,3 @@ void issue_deferred_draw_commands(void) {
         }
     }
 }
-
-
-void render_circle(const CirclePrimitive *circle) {
-    static Vec2 vertices[CIRCLE_VERTICES_MAX];
-    static int prev_num_vertices = 0;
-    static Vec2 prev_position = {0};
-
-    int const num_vertices = MIN((int)circle->radius, CIRCLE_VERTICES_MAX);
-
-    if (prev_num_vertices != num_vertices) {
-        create_circle_geometry(circle->position,
-                               circle->radius,
-                               num_vertices,
-                               vertices);
-        prev_num_vertices = num_vertices;
-        prev_position = circle->position;
-    } else {
-        /* reuse the data, but offset it by difference with previously generated position */
-        /* no evil cos sin ops this way, if radius is shared in sequential calls */
-        Vec2 const d = { prev_position.x - circle->position.x, prev_position.y - circle->position.y };
-        for (int i = 0; i < num_vertices; ++i)
-            vertices[i] = (Vec2){ vertices[i].x - d.x, vertices[i].y - d.y };
-        prev_position = circle->position;
-    }
-
-    VertexBuffer buffer = get_scratch_vertex_array();
-    specify_vertex_buffer(buffer, vertices, sizeof (Vec2) * num_vertices);
-
-    DeferredCommandDraw command = {0};
-
-    command.vertices = (AttributeArrayPointer) {
-        .arity = 2,
-        .type = GL_FLOAT,
-        .stride = sizeof (Vec2),
-        .offset = 0,
-        .buffer = buffer
-    };
-
-    command.constant_colored = true;
-    command.color = circle->color;
-
-    command.element_buffer = get_circle_element_buffer();
-    command.element_count = (num_vertices - 2) * 3;
-    command.range_end = (num_vertices - 2) * 3;
-
-    use_texture_mode(circle->color.a == 255 ? TEXTURE_MODE_OPAQUE : TEXTURE_MODE_GHOSTLY);
-
-    DeferredCommand final_command = {
-        .type = DEFERRED_COMMAND_TYPE_DRAW,
-        .draw = command
-    };
-
-    arrpush(deferred_commands, final_command);
-}
-
-
-void finally_render_quads(const Primitive2D primitives[],
-                          const struct QuadBatch batch,
-                          const VertexBuffer buffer)
-{
-    DeferredCommandDraw command = {0};
-
-    GLsizei off = 0, voff = 0, uvoff = 0, coff = 0;
-
-    if (!batch.constant_colored && batch.textured) {
-        off   = offsetof(ElementIndexedQuad, v1);
-        voff  = offsetof(ElementIndexedQuad, v0);
-        uvoff = offsetof(ElementIndexedQuad, uv0);
-        coff  = offsetof(ElementIndexedQuad, c0);
-    } else if (batch.constant_colored && batch.textured) {
-        off   = offsetof(ElementIndexedQuadWithoutColor, v1);
-        voff  = offsetof(ElementIndexedQuadWithoutColor, v0);
-        uvoff = offsetof(ElementIndexedQuadWithoutColor, uv0);
-    } else if (!batch.constant_colored && !batch.textured) {
-        off   = offsetof(ElementIndexedQuadWithoutTexture, v1);
-        voff  = offsetof(ElementIndexedQuadWithoutTexture, v0);
-        coff  = offsetof(ElementIndexedQuad, c0);
-    } else if (batch.constant_colored && !batch.textured) {
-        off   = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v1);
-        voff  = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v0);
-    }
-
-    command.vertices = (AttributeArrayPointer) {
-        .arity = 2,
-        .type = GL_FLOAT,
-        .stride = off,
-        .offset = voff,
-        .buffer = buffer
-    };
-
-    if (batch.textured)
-        command.texcoords = (AttributeArrayPointer) {
-            .arity = 2,
-            .type = GL_FLOAT,
-            .stride = off,
-            .offset = uvoff,
-            .buffer = buffer
-        };
-
-    if (!batch.constant_colored) {
-        command.colors = (AttributeArrayPointer) {
-            .arity = 4,
-            .type = GL_UNSIGNED_BYTE,
-            .stride = off,
-            .offset = coff,
-            .buffer = buffer
-        };
-    } else {
-        command.constant_colored = true;
-        command.color = primitives[0].sprite.color;
-    }
-
-    if (batch.textured) {
-        command.textured = true;
-        command.texture_key = batch.texture_key;
-        command.texture_repeat = batch.repeat;
-    }
-
-    command.element_buffer = get_quad_element_buffer();
-    command.element_count = 6 * (GLsizei)batch.size;
-    command.range_end = 6 * (GLsizei)batch.size;
-
-    use_texture_mode(batch.mode);
-
-    DeferredCommand final_command = {
-        .type = DEFERRED_COMMAND_TYPE_DRAW,
-        .draw = command
-    };
-
-    arrpush(deferred_commands, final_command);
-}
-
-
-size_t get_quad_payload_size(struct QuadBatch batch) {
-    if (batch.constant_colored && batch.textured)
-        return sizeof (ElementIndexedQuadWithoutColor);
-    else if (!batch.constant_colored && batch.textured)
-        return sizeof (ElementIndexedQuad);
-    else if (batch.constant_colored && !batch.textured)
-        return sizeof (ElementIndexedQuadWithoutColorWithoutTexture);
-    else if (!batch.constant_colored && !batch.textured)
-        return sizeof (ElementIndexedQuadWithoutTexture);
-
-    SDL_assert(false);
-    return 0;
-}
-
-
-bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
-                                                VertexBufferBuilder *builder,
-                                                Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
-                                                Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
-                                                Color color)
-{
-    if (!batch.constant_colored && batch.textured) {
-        ElementIndexedQuad const buffer_element = {
-            .v0 = v0,
-            .v1 = v1,
-            .v2 = v2,
-            .v3 = v3,
-
-            .uv0 = uv0,
-            .uv1 = uv1,
-            .uv2 = uv2,
-            .uv3 = uv3,
-
-            /* equal for all (flat shaded) */
-            .c0 = color,
-            // .c1 = color,
-            .c2 = color,
-            // .c3 = color,
-        };
-
-        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
-
-    } else if (batch.constant_colored && batch.textured) {
-        ElementIndexedQuadWithoutColor const buffer_element = {
-            .v0 = v0,
-            .v1 = v1,
-            .v2 = v2,
-            .v3 = v3,
-
-            .uv0 = uv0,
-            .uv1 = uv1,
-            .uv2 = uv2,
-            .uv3 = uv3,
-        };
-
-        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
-
-    } else if (!batch.constant_colored && !batch.textured) {
-        ElementIndexedQuadWithoutTexture const buffer_element = {
-            .v0 = v0,
-            .v1 = v1,
-            .v2 = v2,
-            .v3 = v3,
-
-            /* equal for all (flat shaded) */
-            .c0 = color,
-            // .c1 = color,
-            .c2 = color,
-            // .c3 = color,
-        };
-
-        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
-
-    } else if (batch.constant_colored && !batch.textured) {
-        ElementIndexedQuadWithoutColorWithoutTexture const buffer_element = {
-            .v0 = v0,
-            .v1 = v1,
-            .v2 = v2,
-            .v3 = v3,
-        };
-
-        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
-    }
-
-    SDL_assert(false);
-    return false;
-}
-
-
-void finally_draw_uncolored_space_traingle_batch(const MeshBatch *batch,
-                                                 const TextureKey texture_key,
-                                                 const VertexBuffer buffer)
-{
-    const size_t primitives_len = arrlenu(batch->primitives);
-
-    /* nothing to do */
-    if (primitives_len == 0)
-        return;
-
-    const Rect srcrect = textures_get_srcrect(&ctx.texture_cache, texture_key);
-    const Rect dims    = textures_get_dims(&ctx.texture_cache, texture_key);
-
-    const float wr = srcrect.w / dims.w;
-    const float hr = srcrect.h / dims.h;
-    const float xr = srcrect.x / dims.w;
-    const float yr = srcrect.y / dims.h;
-
-    /* update pixel-based uvs to correspond with texture atlases */
-    for (size_t i = 0; i < primitives_len; ++i) {
-        UncoloredSpaceTriangle *payload =
-            &((UncoloredSpaceTriangle *)(void *)batch->primitives)[i];
-
-        payload->uv0.x = xr + ((float)payload->uv0.x / srcrect.w) * wr;
-        payload->uv0.y = yr + ((float)payload->uv0.y / srcrect.h) * hr;
-        payload->uv1.x = xr + ((float)payload->uv1.x / srcrect.w) * wr;
-        payload->uv1.y = yr + ((float)payload->uv1.y / srcrect.h) * hr;
-        payload->uv2.x = xr + ((float)payload->uv2.x / srcrect.w) * wr;
-        payload->uv2.y = yr + ((float)payload->uv2.y / srcrect.h) * hr;
-    }
-
-    specify_vertex_buffer(buffer, batch->primitives, primitives_len * sizeof (UncoloredSpaceTriangle));
-
-    DeferredCommandDraw command = {0};
-
-    command.vertices = (AttributeArrayPointer) {
-        .arity = 3,
-        .type = GL_FLOAT,
-        .stride = offsetof(UncoloredSpaceTriangle, v1),
-        .offset = offsetof(UncoloredSpaceTriangle, v0),
-        .buffer = buffer
-    };
-
-    command.texcoords = (AttributeArrayPointer) {
-        .arity = 2,
-        .type = GL_FLOAT,
-        .stride = offsetof(UncoloredSpaceTriangle, v1),
-        .offset = offsetof(UncoloredSpaceTriangle, uv0),
-        .buffer = buffer
-    };
-
-    command.textured = true;
-    command.texture_key = texture_key;
-
-    command.primitive_count = (GLsizei)(3 * primitives_len);
-
-    DeferredCommand final_command = {
-        .type = DEFERRED_COMMAND_TYPE_DRAW,
-        .draw = command
-    };
-
-    arrpush(deferred_commands, final_command);
-}
-
-
-
-bool push_text_payload_to_vertex_buffer_builder(FontData const *font_data,
-                                                VertexBufferBuilder *builder,
-                                                stbtt_aligned_quad quad)
-{
-    (void)font_data;
-
-    ElementIndexedQuadWithoutColor buffer_element = {
-        .v0 = (Vec2){ quad.x0, quad.y0 },
-        .v1 = (Vec2){ quad.x1, quad.y0 },
-        .v2 = (Vec2){ quad.x1, quad.y1 },
-        .v3 = (Vec2){ quad.x0, quad.y1 },
-
-        .uv0 = (Vec2){ quad.s0, quad.t0 },
-        .uv1 = (Vec2){ quad.s1, quad.t0 },
-        .uv2 = (Vec2){ quad.s1, quad.t1 },
-        .uv3 = (Vec2){ quad.s0, quad.t1 },
-    };
-
-    return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
-}
-
-
-void finally_draw_text(FontData const *font_data,
-                       size_t len,
-                       Color color,
-                       VertexBuffer buffer)
-{
-    DeferredCommandDraw command = {0};
-
-    command.vertices = (AttributeArrayPointer) {
-        .arity = 2,
-        .type = GL_FLOAT,
-        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
-        .offset = offsetof(ElementIndexedQuadWithoutColor, v0),
-        .buffer = buffer
-    };
-
-    command.texcoords = (AttributeArrayPointer) {
-        .arity = 2,
-        .type = GL_FLOAT,
-        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
-        .offset = offsetof(ElementIndexedQuadWithoutColor, uv0),
-        .buffer = buffer
-    };
-
-    command.constant_colored = true;
-    command.color = color;
-
-    command.gpu_texture = font_data->texture;
-    command.uses_gpu_key = true;
-    command.textured = true;
-
-    command.element_buffer = get_quad_element_buffer();
-    command.element_count = 6 * (GLsizei)len;
-    command.range_end = 6 * (GLsizei)len;
-
-    use_texture_mode(TEXTURE_MODE_GHOSTLY);
-
-    DeferredCommand final_command = {
-        .type = DEFERRED_COMMAND_TYPE_DRAW,
-        .draw = command
-    };
-
-    arrpush(deferred_commands, final_command);
-
-    /* TODO: why doesn't it get restored if not placed here? */
-    // glDepthMask(GL_TRUE);
-}
-
-
-size_t get_text_payload_size(void) {
-    return sizeof (ElementIndexedQuadWithoutColor);
-}

src/rendering/twn_draw_c.h

@@ -55,16 +55,16 @@ typedef struct RectPrimitive {
 } RectPrimitive;
 
 typedef struct CirclePrimitive {
+    Vec2 position;
     float radius;
     Color color;
-    Vec2 position;
 } CirclePrimitive;
 
 typedef struct TextPrimitive {
-    Color color;
     Vec2 position;
     char *text;
     const char *font;
+    Color color;
     int height_px;
 } TextPrimitive;
 
@@ -76,7 +76,7 @@ typedef enum Primitive2DType {
 } Primitive2DType;
 
 typedef struct Primitive2D {
-    Primitive2DType type;
+    Primitive2DType type; /* TODO: separate to structure of arrays for more efficient memory usage? */
 
     union {
         SpritePrimitive sprite;
@@ -97,6 +97,14 @@ typedef struct UncoloredSpaceTriangle {
     Vec2 uv2; /* in pixels */
 } UncoloredSpaceTriangle;
 
+typedef struct SpaceBillboard {
+    Vec3 position;
+    Vec2 size;
+    Color color;
+    // TextureKey texture; /* is assumed from other places */
+    bool cylindrical;
+} SpaceBillboard;
+
 /* batch of primitives with overlapping properties */
 typedef struct MeshBatch {
     uint8_t *primitives; /* note: interpretation of it is arbitrary */
@@ -179,6 +187,26 @@ typedef struct ElementIndexedQuadWithoutColorWithoutTexture {
     Vec2 v3;
 } ElementIndexedQuadWithoutColorWithoutTexture;
 
+/* TODO: no color variant */
+typedef struct ElementIndexedBillboard {
+    /* upper-left */
+    Vec3 v0;
+    Vec2 uv0;
+    Color c0;
+    /* bottom-left */
+    Vec3 v1;
+    Vec2 uv1;
+    Color c1;
+    /* bottom-right */
+    Vec3 v2;
+    Vec2 uv2;
+    Color c2;
+    /* upper-right */
+    Vec3 v3;
+    Vec2 uv3;
+    Color c3;
+} ElementIndexedBillboard;
+
 
 /* renders the background, then the primitives in all render queues */
 void render(void);
@@ -207,9 +235,6 @@ struct QuadBatch collect_rect_batch(const Primitive2D primitives[], size_t len);
 void render_sprite_batch(const Primitive2D primitives[], struct QuadBatch batch);
 void render_rect_batch(const Primitive2D primitives[], struct QuadBatch batch);
 
-void draw_uncolored_space_traingle_batch(MeshBatch *batch,
-                                         TextureKey texture_key);
-
 /* text */
 
 void render_text(const TextPrimitive *text);
@@ -280,8 +305,10 @@ bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
                                                 Color color);
 
 void finally_draw_uncolored_space_traingle_batch(MeshBatch const *batch,
-                                                 TextureKey texture_key,
-                                                 VertexBuffer buffer);
+                                                 TextureKey texture_key);
+
+void finally_draw_billboard_batch(MeshBatch const *batch,
+                                  TextureKey texture_key);
 
 size_t get_text_payload_size(void);
 

src/rendering/twn_gl_15_rendering.c

@@ -452,6 +452,7 @@ void finally_draw_command(DeferredCommandDraw command) {
                        command.colors.type,
                        command.colors.stride,
                        (void *)command.colors.offset);
+
     } else if (command.constant_colored)
         glColor4ub(command.color.r,
                    command.color.g,

src/rendering/twn_quads.c

@@ -1,30 +1,171 @@
 #include "twn_draw_c.h"
 
+#include <stb_ds.h>
+
 #include <stddef.h>
 
 
-struct QuadBatch collect_quad_batch(const Primitive2D primitives[], size_t len) {
-    if (primitives[0].type == PRIMITIVE_2D_SPRITE)
-        return collect_sprite_batch(primitives, len);
-    else if (primitives[0].type == PRIMITIVE_2D_RECT)
-        return collect_rect_batch(primitives, len);
-    else
-        SDL_assert(false);
-
-    return (struct QuadBatch){0};
-}
-
-
-/* assumes that orthogonal matrix setup is done already */
-void render_quad_batch(const Primitive2D primitives[],
-                       const struct QuadBatch batch)
+void finally_render_quads(const Primitive2D primitives[],
+                          const struct QuadBatch batch,
+                          const VertexBuffer buffer)
 {
-    if (primitives[0].type == PRIMITIVE_2D_SPRITE)
-        render_sprite_batch(primitives, batch);
-    else if (primitives[0].type == PRIMITIVE_2D_RECT)
-        render_rect_batch(primitives, batch);
-    else
-        SDL_assert(false);
+    DeferredCommandDraw command = {0};
 
-    return (struct QuadBatch){0};
+    GLsizei off = 0, voff = 0, uvoff = 0, coff = 0;
+
+    if (!batch.constant_colored && batch.textured) {
+        off   = offsetof(ElementIndexedQuad, v1);
+        voff  = offsetof(ElementIndexedQuad, v0);
+        uvoff = offsetof(ElementIndexedQuad, uv0);
+        coff  = offsetof(ElementIndexedQuad, c0);
+    } else if (batch.constant_colored && batch.textured) {
+        off   = offsetof(ElementIndexedQuadWithoutColor, v1);
+        voff  = offsetof(ElementIndexedQuadWithoutColor, v0);
+        uvoff = offsetof(ElementIndexedQuadWithoutColor, uv0);
+    } else if (!batch.constant_colored && !batch.textured) {
+        off   = offsetof(ElementIndexedQuadWithoutTexture, v1);
+        voff  = offsetof(ElementIndexedQuadWithoutTexture, v0);
+        coff  = offsetof(ElementIndexedQuad, c0);
+    } else if (batch.constant_colored && !batch.textured) {
+        off   = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v1);
+        voff  = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v0);
+    }
+
+    command.vertices = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = off,
+        .offset = voff,
+        .buffer = buffer
+    };
+
+    if (batch.textured)
+        command.texcoords = (AttributeArrayPointer) {
+            .arity = 2,
+            .type = GL_FLOAT,
+            .stride = off,
+            .offset = uvoff,
+            .buffer = buffer
+        };
+
+    if (!batch.constant_colored) {
+        command.colors = (AttributeArrayPointer) {
+            .arity = 4,
+            .type = GL_UNSIGNED_BYTE,
+            .stride = off,
+            .offset = coff,
+            .buffer = buffer
+        };
+    } else {
+        command.constant_colored = true;
+        command.color = primitives[0].sprite.color;
+    }
+
+    if (batch.textured) {
+        command.textured = true;
+        command.texture_key = batch.texture_key;
+        command.texture_repeat = batch.repeat;
+    }
+
+    command.element_buffer = get_quad_element_buffer();
+    command.element_count = 6 * (GLsizei)batch.size;
+    command.range_end = 6 * (GLsizei)batch.size;
+
+    use_texture_mode(batch.mode);
+
+    DeferredCommand final_command = {
+        .type = DEFERRED_COMMAND_TYPE_DRAW,
+        .draw = command
+    };
+
+    arrpush(deferred_commands, final_command);
+}
+
+
+size_t get_quad_payload_size(struct QuadBatch batch) {
+    if (batch.constant_colored && batch.textured)
+        return sizeof (ElementIndexedQuadWithoutColor);
+    else if (!batch.constant_colored && batch.textured)
+        return sizeof (ElementIndexedQuad);
+    else if (batch.constant_colored && !batch.textured)
+        return sizeof (ElementIndexedQuadWithoutColorWithoutTexture);
+    else if (!batch.constant_colored && !batch.textured)
+        return sizeof (ElementIndexedQuadWithoutTexture);
+
+    SDL_assert(false);
+    return 0;
+}
+
+
+bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
+                                                VertexBufferBuilder *builder,
+                                                Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
+                                                Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
+                                                Color color)
+{
+    if (!batch.constant_colored && batch.textured) {
+        ElementIndexedQuad const buffer_element = {
+            .v0 = v0,
+            .v1 = v1,
+            .v2 = v2,
+            .v3 = v3,
+
+            .uv0 = uv0,
+            .uv1 = uv1,
+            .uv2 = uv2,
+            .uv3 = uv3,
+
+            /* equal for all (flat shaded) */
+            .c0 = color,
+            // .c1 = color,
+            .c2 = color,
+            // .c3 = color,
+        };
+
+        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
+
+    } else if (batch.constant_colored && batch.textured) {
+        ElementIndexedQuadWithoutColor const buffer_element = {
+            .v0 = v0,
+            .v1 = v1,
+            .v2 = v2,
+            .v3 = v3,
+
+            .uv0 = uv0,
+            .uv1 = uv1,
+            .uv2 = uv2,
+            .uv3 = uv3,
+        };
+
+        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
+
+    } else if (!batch.constant_colored && !batch.textured) {
+        ElementIndexedQuadWithoutTexture const buffer_element = {
+            .v0 = v0,
+            .v1 = v1,
+            .v2 = v2,
+            .v3 = v3,
+
+            /* equal for all (flat shaded) */
+            .c0 = color,
+            // .c1 = color,
+            .c2 = color,
+            // .c3 = color,
+        };
+
+        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
+
+    } else if (batch.constant_colored && !batch.textured) {
+        ElementIndexedQuadWithoutColorWithoutTexture const buffer_element = {
+            .v0 = v0,
+            .v1 = v1,
+            .v2 = v2,
+            .v3 = v3,
+        };
+
+        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
+    }
+
+    SDL_assert(false);
+    return false;
 }

src/rendering/twn_skybox.c

@@ -21,6 +21,8 @@ void render_skybox(void) {
     if (!paths_in_use)
         return;
 
+    use_space_pipeline();
+
     /* note: ownership of 'paths_in_use' goes there */
     DeferredCommand command = {
         .type = DEFERRED_COMMAND_TYPE_DRAW_SKYBOX,

src/rendering/twn_text.c

@@ -175,7 +175,7 @@ static void text_draw_with(FontData* font_data, char* text, Vec2 position, Color
 
     const size_t len = SDL_strlen(text);
 
-    VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_text_payload_size() * len);
+    VertexBufferBuilder payload = build_vertex_buffer(vertex_array, sizeof (ElementIndexedQuadWithoutColor) * len);
 
     for (size_t i = 0; i < len; ++i) {
         const char c = text[i];
@@ -318,3 +318,73 @@ float draw_text_width(const char *string, float height, const char *font) {
     
     return (float)length * font_data->scale_factor;
 }
+
+
+bool push_text_payload_to_vertex_buffer_builder(FontData const *font_data,
+                                                VertexBufferBuilder *builder,
+                                                stbtt_aligned_quad quad)
+{
+    (void)font_data;
+
+    ElementIndexedQuadWithoutColor buffer_element = {
+        .v0 = (Vec2){ quad.x0, quad.y0 },
+        .v1 = (Vec2){ quad.x1, quad.y0 },
+        .v2 = (Vec2){ quad.x1, quad.y1 },
+        .v3 = (Vec2){ quad.x0, quad.y1 },
+
+        .uv0 = (Vec2){ quad.s0, quad.t0 },
+        .uv1 = (Vec2){ quad.s1, quad.t0 },
+        .uv2 = (Vec2){ quad.s1, quad.t1 },
+        .uv3 = (Vec2){ quad.s0, quad.t1 },
+    };
+
+    return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
+}
+
+
+void finally_draw_text(FontData const *font_data,
+                       size_t len,
+                       Color color,
+                       VertexBuffer buffer)
+{
+    DeferredCommandDraw command = {0};
+
+    command.vertices = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
+        .offset = offsetof(ElementIndexedQuadWithoutColor, v0),
+        .buffer = buffer
+    };
+
+    command.texcoords = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
+        .offset = offsetof(ElementIndexedQuadWithoutColor, uv0),
+        .buffer = buffer
+    };
+
+    command.constant_colored = true;
+    command.color = color;
+
+    command.gpu_texture = font_data->texture;
+    command.uses_gpu_key = true;
+    command.textured = true;
+
+    command.element_buffer = get_quad_element_buffer();
+    command.element_count = 6 * (GLsizei)len;
+    command.range_end = 6 * (GLsizei)len;
+
+    use_texture_mode(TEXTURE_MODE_GHOSTLY);
+
+    DeferredCommand final_command = {
+        .type = DEFERRED_COMMAND_TYPE_DRAW,
+        .draw = command
+    };
+
+    arrpush(deferred_commands, final_command);
+
+    /* TODO: why doesn't it get restored if not placed here? */
+    // glDepthMask(GL_TRUE);
+}

src/rendering/twn_triangles.c

@@ -17,6 +17,7 @@ void draw_triangle(const char *path,
                    Vec2 uv1,
                    Vec2 uv2)
 {
+    // TODO: order drawing by atlas id as well, so that texture rebinding is not as common
     const TextureKey texture_key = textures_get_key(&ctx.texture_cache, path);
 
     struct MeshBatchItem *batch_p = hmgetp_null(ctx.uncolored_mesh_batches, texture_key);
@@ -42,10 +43,67 @@ void draw_triangle(const char *path,
 }
 
 
-void draw_uncolored_space_traingle_batch(struct MeshBatch *batch,
-                                         TextureKey texture_key)
+void finally_draw_uncolored_space_traingle_batch(const MeshBatch *batch,
+                                                 const TextureKey texture_key)
 {
-    VertexBuffer const vertex_array = get_scratch_vertex_array();
+    const size_t primitives_len = arrlenu(batch->primitives);
 
-    finally_draw_uncolored_space_traingle_batch(batch, texture_key, vertex_array);
+    /* nothing to do */
+    if (primitives_len == 0)
+        return;
+
+    VertexBuffer const buffer = get_scratch_vertex_array();
+
+    const Rect srcrect = textures_get_srcrect(&ctx.texture_cache, texture_key);
+    const Rect dims    = textures_get_dims(&ctx.texture_cache, texture_key);
+
+    const float wr = srcrect.w / dims.w;
+    const float hr = srcrect.h / dims.h;
+    const float xr = srcrect.x / dims.w;
+    const float yr = srcrect.y / dims.h;
+
+    /* update pixel-based uvs to correspond with texture atlases */
+    for (size_t i = 0; i < primitives_len; ++i) {
+        UncoloredSpaceTriangle *payload =
+            &((UncoloredSpaceTriangle *)(void *)batch->primitives)[i];
+
+        payload->uv0.x = xr + ((float)payload->uv0.x / srcrect.w) * wr;
+        payload->uv0.y = yr + ((float)payload->uv0.y / srcrect.h) * hr;
+        payload->uv1.x = xr + ((float)payload->uv1.x / srcrect.w) * wr;
+        payload->uv1.y = yr + ((float)payload->uv1.y / srcrect.h) * hr;
+        payload->uv2.x = xr + ((float)payload->uv2.x / srcrect.w) * wr;
+        payload->uv2.y = yr + ((float)payload->uv2.y / srcrect.h) * hr;
+    }
+
+    specify_vertex_buffer(buffer, batch->primitives, primitives_len * sizeof (UncoloredSpaceTriangle));
+
+    DeferredCommandDraw command = {0};
+
+    command.vertices = (AttributeArrayPointer) {
+        .arity = 3,
+        .type = GL_FLOAT,
+        .stride = offsetof(UncoloredSpaceTriangle, v1),
+        .offset = offsetof(UncoloredSpaceTriangle, v0),
+        .buffer = buffer
+    };
+
+    command.texcoords = (AttributeArrayPointer) {
+        .arity = 2,
+        .type = GL_FLOAT,
+        .stride = offsetof(UncoloredSpaceTriangle, v1),
+        .offset = offsetof(UncoloredSpaceTriangle, uv0),
+        .buffer = buffer
+    };
+
+    command.textured = true;
+    command.texture_key = texture_key;
+
+    command.primitive_count = (GLsizei)(3 * primitives_len);
+
+    DeferredCommand final_command = {
+        .type = DEFERRED_COMMAND_TYPE_DRAW,
+        .draw = command
+    };
+
+    arrpush(deferred_commands, final_command);
 }

src/twn_amalgam.c

@@ -17,4 +17,6 @@
 #include "rendering/twn_sprites.c"
 #include "rendering/twn_rects.c"
 #include "rendering/twn_text.c"
+#include "rendering/twn_quads.c"
 #include "rendering/twn_triangles.c"
+#include "rendering/twn_billboards.c"

src/twn_camera.c

@@ -28,9 +28,10 @@ Matrix4 camera_look_at(const Camera *const camera) {
     result.row[3].x = -m_vec_dot(r, camera->pos);
     result.row[3].y = -m_vec_dot(u, camera->pos);
     result.row[3].z =  m_vec_dot(camera->target, camera->pos);
-    result.row[0].w =  result.row[1].w = result.row[2].w = 0.0f;
     result.row[3].w =  1.0f;
 
+    result.row[0].w =  result.row[1].w = result.row[2].w = 0.0f;
+
     return result;
 }
 

src/twn_engine_context_c.h

@@ -47,6 +47,7 @@ typedef struct EngineContext {
     /* rendering */
     Primitive2D *render_queue_2d;
     MeshBatchItem *uncolored_mesh_batches;
+    MeshBatchItem *billboard_batches;
     TextCache text_cache;
     TextureCache texture_cache;