don't use depth range hack in rect case

CMakeLists.txt

@@ -104,6 +104,7 @@ set(TWN_NONOPT_SOURCE_FILES
 
         src/rendering/twn_draw.c src/rendering/twn_draw_c.h
         src/rendering/twn_sprites.c
+        src/rendering/twn_rects.c
         src/rendering/twn_text.c
         src/rendering/twn_triangles.c
         src/rendering/twn_circles.c

include/twn_texture_modes.h

@@ -1,6 +1,9 @@
 #ifndef TWN_TEXTURES_MODES_H
 #define TWN_TEXTURES_MODES_H
 
+/* TODO: rename, as it doesn't have to be about textures only, but blending */
+/* TODO: move from public /include/ tree */
+
 /* alpha channel information */
 typedef enum TextureMode {
     TEXTURE_MODE_OPAQUE,        /* all pixels are solid */

src/rendering/twn_draw.c

@@ -35,22 +35,6 @@ void render_queue_clear(void) {
 }
 
 
-/* rectangle */
-void draw_rectangle(Rect rect, Color color) {
-    RectPrimitive rectangle = {
-        .rect = rect,
-        .color = color,
-    };
-
-    Primitive2D primitive = {
-        .type = PRIMITIVE_2D_RECT,
-        .rect = rectangle,
-    };
-
-    arrput(ctx.render_queue_2d, primitive);
-}
-
-
 void draw_9slice(const char *texture_path, int texture_w, int texture_h, int border_thickness, Rect rect, Color color) {
     const float bt = (float)border_thickness; /* i know! */
     const float bt2 = bt * 2; /* combined size of the two borders in an axis */
@@ -204,19 +188,25 @@ static void render_2d(void) {
 
         switch (current->type) {
             case PRIMITIVE_2D_SPRITE: {
-                const struct SpriteBatch batch =
+                const struct QuadBatch batch =
                     collect_sprite_batch(current, render_queue_len - i);
 
                 /* TODO: what's even the point? just use OR_EQUAL comparison */
                 set_depth_range((double)batch_count / UINT16_MAX, 1.0);
-                render_sprites(current, batch);
+                render_sprite_batch(current, batch);
 
                 i += batch.size - 1; ++batch_count;
                 break;
             }
-            case PRIMITIVE_2D_RECT:
+            case PRIMITIVE_2D_RECT: {
-                render_rectangle(&current->rect);
+                const struct QuadBatch batch =
+                    collect_rect_batch(current, render_queue_len - i);
+
+                render_rect_batch(current, batch);
+
+                i += batch.size - 1; ++batch_count;
                 break;
+            }
             case PRIMITIVE_2D_CIRCLE:
                 render_circle(&current->circle);
                 break;

src/rendering/twn_draw_c.h

@@ -135,15 +135,18 @@ void create_circle_geometry(Vec2 position,
                             SDL_Vertex vertices[],
                             int indices[]);
 
-struct SpriteBatch {
+struct QuadBatch {
     size_t size;             /* how many primitives are in current batch */
-    TextureMode mode;
+    TextureMode mode;        /* how color should be applied */
     bool constant_colored;   /* whether colored batch is uniformly colored */
     bool repeat;             /* whether repeat is needed */
-} collect_sprite_batch(const Primitive2D primitives[], size_t len);
+    bool textured;
-
+} collect_quad_batch(const Primitive2D primitives[], size_t len);
-void render_sprites(const Primitive2D primitives[],
+void render_quad_batch(const Primitive2D primitives[], struct QuadBatch batch);
-                    const struct SpriteBatch batch);
+struct QuadBatch collect_sprite_batch(const Primitive2D primitives[], size_t len);
+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);
@@ -164,14 +167,14 @@ VertexBuffer create_vertex_buffer(void);
 
 void delete_vertex_buffer(VertexBuffer buffer);
 
-void specify_vertex_buffer(VertexBuffer buffer, void *data, size_t bytes);
+void specify_vertex_buffer(VertexBuffer buffer, void const *data, size_t bytes);
 
 /* uses present in 1.5 buffer mapping feature */
 VertexBufferBuilder build_vertex_buffer(VertexBuffer buffer, size_t bytes);
 
 /* collects bytes for sending to the gpu until all is pushed, which is when false is returned */
 bool push_to_vertex_buffer_builder(VertexBufferBuilder *builder,
-                                   void *bytes,
+                                   void const *bytes,
                                    size_t size);
 
 /* state */
@@ -196,19 +199,17 @@ void use_2d_pipeline(void);
 
 void use_texture_mode(TextureMode mode);
 
-void upload_quad_vertices(Rect rect);
+void finally_render_quads(Primitive2D const primitives[],
+                          struct QuadBatch batch,
+                          VertexBuffer buffer);
 
-void finally_render_sprites(Primitive2D const primitives[],
+size_t get_quad_payload_size(struct QuadBatch batch);
-                            struct SpriteBatch batch,
-                            VertexBuffer buffer);
 
-size_t get_sprite_payload_size(struct SpriteBatch batch);
+bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
-
+                                                VertexBufferBuilder *builder,
-bool push_sprite_payload_to_vertex_buffer_builder(struct SpriteBatch batch,
+                                                Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
-                                                  VertexBufferBuilder *builder,
+                                                Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
-                                                  Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
+                                                Color color);
-                                                  Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
-                                                  Color color);
 
 void finally_draw_uncolored_space_traingle_batch(MeshBatch const *batch,
                                                  TextureKey texture_key,

src/rendering/twn_gl_15_rendering.c

@@ -3,6 +3,7 @@
 #include "twn_util_c.h"
 #include "twn_engine_context_c.h"
 #include "twn_text_c.h"
+#include "twn_types.h"
 
 #include <glad/glad.h>
 #include <stb_ds.h>
@@ -48,6 +49,34 @@ typedef struct ElementIndexedQuadWithoutColor {
 } ElementIndexedQuadWithoutColor;
 
 
+typedef struct ElementIndexedQuadWithoutTexture {
+    /* upper-left */
+    Vec2 v0;
+    Color c0;
+    /* bottom-left */
+    Vec2 v1;
+    Color c1;
+    /* bottom-right */
+    Vec2 v2;
+    Color c2;
+    /* upper-right */
+    Vec2 v3;
+    Color c3;
+} ElementIndexedQuadWithoutTexture;
+
+
+typedef struct ElementIndexedQuadWithoutColorWithoutTexture {
+    /* upper-left */
+    Vec2 v0;
+    /* bottom-left */
+    Vec2 v1;
+    /* bottom-right */
+    Vec2 v2;
+    /* upper-right */
+    Vec2 v3;
+} ElementIndexedQuadWithoutColorWithoutTexture;
+
+
 typedef enum {
     PIPELINE_NO,
     PIPELINE_SPACE,
@@ -139,33 +168,6 @@ void use_2d_pipeline(void) {
 }
 
 
-void upload_quad_vertices(Rect rect) {
-    /* client memory needs to be reachable on glDraw*, so */
-    static float vertices[6 * 2];
-
-    vertices[0]  = rect.x;          vertices[1]  = rect.y;
-    vertices[2]  = rect.x;          vertices[3]  = rect.y + rect.h;
-    vertices[4]  = rect.x + rect.w; vertices[5]  = rect.y + rect.h;
-    vertices[6]  = rect.x + rect.w; vertices[7]  = rect.y + rect.h;
-    vertices[8]  = rect.x + rect.w; vertices[9]  = rect.y;
-    vertices[10] = rect.x;          vertices[11] = rect.y;
-
-    glVertexPointer(2, GL_FLOAT, 0, (void *)&vertices);
-}
-
-
-void render_rectangle(const RectPrimitive *rectangle) {
-    glColor4ub(rectangle->color.r, rectangle->color.g,
-               rectangle->color.b, rectangle->color.a);
-
-    glEnableClientState(GL_VERTEX_ARRAY);
-    upload_quad_vertices(rectangle->rect);
-
-    glDrawArrays(GL_TRIANGLES, 0, 6);
-    glDisableClientState(GL_VERTEX_ARRAY);
-}
-
-
 void render_circle(const CirclePrimitive *circle) {
     static SDL_Vertex vertices[CIRCLE_VERTICES_MAX];
     static int indices[CIRCLE_VERTICES_MAX * 3];
@@ -258,7 +260,7 @@ VertexBufferBuilder build_vertex_buffer(VertexBuffer buffer, size_t bytes) {
 
 
 bool push_to_vertex_buffer_builder(VertexBufferBuilder *builder,
-                                   void *bytes, size_t size) {
+                                   void const *bytes, size_t size) {
     if (builder->bytes_left == 0)
         return false;
 
@@ -277,24 +279,30 @@ bool push_to_vertex_buffer_builder(VertexBufferBuilder *builder,
 }
 
 
-void finally_render_sprites(const Primitive2D primitives[],
+void finally_render_quads(const Primitive2D primitives[],
-                            const struct SpriteBatch batch,
+                          const struct QuadBatch batch,
-                            const VertexBuffer buffer)
+                          const VertexBuffer buffer)
 {
     (void)buffer;
 
-    GLsizei off;
+    GLsizei off = 0, voff = 0, uvoff = 0, coff = 0;
-    GLsizei voff;
-    GLsizei uvoff;
 
-    if (!batch.constant_colored) {
+    if (!batch.constant_colored && batch.textured) {
         off   = offsetof(ElementIndexedQuad, v1);
         voff  = offsetof(ElementIndexedQuad, v0);
         uvoff = offsetof(ElementIndexedQuad, uv0);
-    } else {
+        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);
     }
 
     /* vertex specification */
@@ -304,65 +312,82 @@ void finally_render_sprites(const Primitive2D primitives[],
                     off,
                     (void *)(size_t)voff);
 
-    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
+    if (batch.textured) {
-    glClientActiveTexture(GL_TEXTURE0);
+        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
-    glTexCoordPointer(2,
+        glClientActiveTexture(GL_TEXTURE0);
-                      GL_FLOAT,
+        glTexCoordPointer(2,
-                      off,
+                          GL_FLOAT,
-                      (void *)(size_t)uvoff);
+                          off,
+                          (void *)(size_t)uvoff);
+    }
 
     if (!batch.constant_colored) {
         glEnableClientState(GL_COLOR_ARRAY);
         glColorPointer(4,
                        GL_UNSIGNED_BYTE,
                        off,
-                       (void *)offsetof(ElementIndexedQuad, c0));
+                       (void *)(size_t)coff);
     } else
         glColor4ub(primitives[0].sprite.color.r,
                    primitives[0].sprite.color.g,
                    primitives[0].sprite.color.b,
                    primitives[0].sprite.color.a);
 
-    if (!batch.repeat)
+    if (batch.textured) {
-        textures_bind(&ctx.texture_cache, primitives->sprite.texture_key);
+        if (!batch.repeat)
-    else
+            textures_bind(&ctx.texture_cache, primitives->sprite.texture_key);
-        textures_bind_repeating(&ctx.texture_cache, primitives->sprite.texture_key);
+        else
+            textures_bind_repeating(&ctx.texture_cache, primitives->sprite.texture_key);
+    }
 
     bind_quad_element_buffer();
 
     glDrawElements(GL_TRIANGLES, 6 * (GLsizei)batch.size, GL_UNSIGNED_SHORT, NULL);
 
     /* clear the state */
-    glBufferData(GL_ARRAY_BUFFER, 0, NULL, GL_STREAM_DRAW);
+    {
-    glBindBuffer(GL_ARRAY_BUFFER, 0);
+        glBufferData(GL_ARRAY_BUFFER, 0, NULL, GL_STREAM_DRAW);
+        glBindBuffer(GL_ARRAY_BUFFER, 0);
 
-    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+        if (batch.textured)
-    glDisableClientState(GL_VERTEX_ARRAY);
+            glDisableClientState(GL_TEXTURE_COORD_ARRAY);
 
-    if (!batch.constant_colored)
+        glDisableClientState(GL_VERTEX_ARRAY);
-        glDisableClientState(GL_COLOR_ARRAY);
 
-    glBindTexture(GL_TEXTURE_2D, 0);
+        if (!batch.constant_colored)
-    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+            glDisableClientState(GL_COLOR_ARRAY);
+
+        if (batch.textured)
+            glBindTexture(GL_TEXTURE_2D, 0);
+
+        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+    }
 }
 
 
-size_t get_sprite_payload_size(struct SpriteBatch batch) {
+size_t get_quad_payload_size(struct QuadBatch batch) {
-    if (batch.constant_colored)
+    if (batch.constant_colored && batch.textured)
         return sizeof (ElementIndexedQuadWithoutColor);
-    else
+    else if (!batch.constant_colored && batch.textured)
         return sizeof (ElementIndexedQuad);
+    else if (batch.constant_colored && !batch.textured)
+        return sizeof (ElementIndexedQuadWithoutTexture);
+    else if (!batch.constant_colored && !batch.textured)
+        return sizeof (ElementIndexedQuadWithoutColorWithoutTexture);
+
+    SDL_assert(false);
+    return 0;
 }
 
 
-bool push_sprite_payload_to_vertex_buffer_builder(struct SpriteBatch batch,
+bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
-                                                  VertexBufferBuilder *builder,
+                                                VertexBufferBuilder *builder,
-                                                  Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
+                                                Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
-                                                  Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
+                                                Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
-                                                  Color color)
+                                                Color color)
 {
-    if (!batch.constant_colored) {
+    if (!batch.constant_colored && batch.textured) {
-        ElementIndexedQuad buffer_element = {
+        ElementIndexedQuad const buffer_element = {
             .v0 = v0,
             .v1 = v1,
             .v2 = v2,
@@ -382,8 +407,8 @@ bool push_sprite_payload_to_vertex_buffer_builder(struct SpriteBatch batch,
 
         return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
 
-    } else {
+    } else if (batch.constant_colored && batch.textured) {
-        ElementIndexedQuadWithoutColor buffer_element = {
+        ElementIndexedQuadWithoutColor const buffer_element = {
             .v0 = v0,
             .v1 = v1,
             .v2 = v2,
@@ -395,8 +420,37 @@ bool push_sprite_payload_to_vertex_buffer_builder(struct SpriteBatch batch,
             .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_gl_any_rendering.c

@@ -26,7 +26,7 @@ void delete_vertex_buffer(VertexBuffer buffer) {
 }
 
 
-void specify_vertex_buffer(VertexBuffer buffer, void *data, size_t bytes) {
+void specify_vertex_buffer(VertexBuffer buffer, void const *data, size_t bytes) {
     glBindBuffer(GL_ARRAY_BUFFER, buffer);
     glBufferData(GL_ARRAY_BUFFER, bytes, data, GL_STREAM_DRAW);
 }
@@ -74,6 +74,9 @@ void clear_draw_buffer(void) {
     /* TODO: don't clear color when skybox is applied? */
     /*       for that window should match framebuffer */
     /*       also it is driver dependent, from what i can gather */
+    /* INFO: also, based on below, driver might prefer it staying this way */
+    /*       https://gamedev.stackexchange.com/questions/90344/render-with-const-depth-value */
+    /*       we could optionally load ARB_invalidate_subdata extension if it's available instead */
     glClear(GL_COLOR_BUFFER_BIT |
             GL_DEPTH_BUFFER_BIT |
             GL_STENCIL_BUFFER_BIT);

src/rendering/twn_quads.c

@@ -0,0 +1,30 @@
+#include "twn_draw_c.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)
+{
+    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);
+
+    return (struct QuadBatch){0};
+}

src/rendering/twn_rects.c

@@ -0,0 +1,104 @@
+#include "twn_draw.h"
+#include "twn_draw_c.h"
+#include "twn_engine_context_c.h"
+#include "twn_util.h"
+#include "twn_util_c.h"
+#include "twn_textures_c.h"
+#include "twn_option.h"
+
+#include <stb_ds.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+
+
+void draw_rectangle(Rect rect, Color color) {
+    RectPrimitive rectangle = {
+        .rect = rect,
+        .color = color,
+    };
+
+    Primitive2D primitive = {
+        .type = PRIMITIVE_2D_RECT,
+        .rect = rectangle,
+    };
+
+    arrput(ctx.render_queue_2d, primitive);
+}
+
+
+struct QuadBatch collect_rect_batch(const Primitive2D primitives[], size_t len) {
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_RECT);
+    SDL_assert(primitives && len != 0);
+
+    struct QuadBatch batch = {
+        .mode = primitives[0].rect.color.a == 255 ? TEXTURE_MODE_OPAQUE : TEXTURE_MODE_GHOSTLY,
+        .constant_colored = true,
+    };
+
+    const uint32_t uniform_color = *(const uint32_t *)&primitives[0].rect.color;
+
+    /* batch size is clamped so that reallocated short indices could be used */
+    if (len >= QUAD_ELEMENT_BUFFER_LENGTH)
+        len = QUAD_ELEMENT_BUFFER_LENGTH;
+
+    for (size_t i = 0; i < len; ++i) {
+        const Primitive2D *const current = &primitives[i];
+
+        /* don't touch things other than rectangles */
+        if (current->type != PRIMITIVE_2D_RECT)
+            break;
+
+        /* only collect the same blend modes */
+        if ((current->rect.color.a == 255 ? TEXTURE_MODE_OPAQUE : TEXTURE_MODE_GHOSTLY) != batch.mode)
+            break;
+
+        /* if all are modulated the same we can skip sending the color data */
+        if (*(const uint32_t *)&current->rect.color != uniform_color)
+            batch.constant_colored = false;
+
+        ++batch.size;
+    }
+
+    return batch;
+}
+
+
+/* assumes that orthogonal matrix setup is done already */
+void render_rect_batch(const Primitive2D primitives[],
+                       const struct QuadBatch batch)
+{
+    SDL_assert(primitives && batch.size != 0);
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_RECT);
+
+    /* single vertex array is used for every batch with NULL glBufferData() trick at the end */
+    static VertexBuffer vertex_array = 0;
+    if (vertex_array == 0)
+        vertex_array = create_vertex_buffer();
+
+    use_texture_mode(batch.mode);
+
+    /* vertex population over a vertex buffer builder interface */
+    {
+        VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_quad_payload_size(batch) * batch.size);
+
+        for (size_t i = 0; i < batch.size; ++i) {
+            /* render opaques front to back, to gain benefit of an early z rejection */
+            const size_t cur = batch.mode == TEXTURE_MODE_GHOSTLY ? i : batch.size - i - 1;
+            const RectPrimitive rect = primitives[cur].rect;
+
+            Vec2 v0 = { rect.rect.x,          rect.rect.y };
+            Vec2 v1 = { rect.rect.x,          rect.rect.y + rect.rect.h };
+            Vec2 v2 = { rect.rect.x + rect.rect.w, rect.rect.y + rect.rect.h };
+            Vec2 v3 = { rect.rect.x + rect.rect.w, rect.rect.y };
+
+            push_quad_payload_to_vertex_buffer_builder(
+                batch, &payload,
+                v0, v1, v2, v3,
+                (Vec2){0}, (Vec2){0}, (Vec2){0}, (Vec2){0},
+                rect.color);
+        }
+    }
+
+    finally_render_quads(primitives, batch, vertex_array);
+}

src/rendering/twn_sprites.c

@@ -60,15 +60,18 @@ void draw_sprite_args(const DrawSpriteArgs args) {
 }
 
 
-struct SpriteBatch collect_sprite_batch(const Primitive2D primitives[], size_t len) {
+struct QuadBatch collect_sprite_batch(const Primitive2D primitives[], size_t len) {
-    /* assumes that first primitive is already a sprite */
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_SPRITE);
+    SDL_assert(primitives && len != 0);
+
     const uint16_t texture_key_id = primitives[0].sprite.texture_key.id;
     const int atlas_id = textures_get_atlas_id(&ctx.texture_cache, primitives[0].sprite.texture_key);
 
-    struct SpriteBatch batch = {
+    struct QuadBatch batch = {
         .mode = textures_get_mode(&ctx.texture_cache, primitives[0].sprite.texture_key),
         .constant_colored = true,
         .repeat = primitives[0].sprite.repeat,
+        .textured = true,
     };
 
     const uint32_t uniform_color = *(const uint32_t *)&primitives[0].sprite.color;
@@ -116,9 +119,12 @@ struct SpriteBatch collect_sprite_batch(const Primitive2D primitives[], size_t l
 
 
 /* assumes that orthogonal matrix setup is done already */
-void render_sprites(const Primitive2D primitives[],
+void render_sprite_batch(const Primitive2D primitives[],
-                    const struct SpriteBatch batch)
+                         const struct QuadBatch batch)
 {
+    SDL_assert(primitives && batch.size != 0);
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_SPRITE);
+
     /* single vertex array is used for every batch with NULL glBufferData() trick at the end */
     static VertexBuffer vertex_array = 0;
     if (vertex_array == 0)
@@ -131,10 +137,10 @@ void render_sprites(const Primitive2D primitives[],
 
     /* vertex population over a vertex buffer builder interface */
     {
-        VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_sprite_payload_size(batch) * batch.size);
+        VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_quad_payload_size(batch) * batch.size);
 
         for (size_t i = 0; i < batch.size; ++i) {
-            /* render opaques front to back */
+            /* render opaques front to back, to gain benefit of an early z rejection */
             const size_t cur = batch.mode == TEXTURE_MODE_GHOSTLY ? i : batch.size - i - 1;
             const SpritePrimitive sprite = primitives[cur].sprite;
 
@@ -233,9 +239,9 @@ void render_sprites(const Primitive2D primitives[],
                 v3 = (Vec2){ c.x + t.x * +h.x - t.y * -h.y, c.y + t.y * +h.x + t.x * -h.y };
             }
 
-            push_sprite_payload_to_vertex_buffer_builder(batch, &payload, v0, v1, v2, v3, uv0, uv1, uv2, uv3, sprite.color);
+            push_quad_payload_to_vertex_buffer_builder(batch, &payload, v0, v1, v2, v3, uv0, uv1, uv2, uv3, sprite.color);
         }
     }
 
-    finally_render_sprites(primitives, batch, vertex_array);
+    finally_render_quads(primitives, batch, vertex_array);
 }

src/twn_amalgam.c

@@ -15,5 +15,6 @@
 #include "rendering/twn_fog.c"
 #include "rendering/twn_skybox.c"
 #include "rendering/twn_sprites.c"
+#include "rendering/twn_rects.c"
 #include "rendering/twn_text.c"
 #include "rendering/twn_triangles.c"