twn_draw: texture_region option for draw_billboard()

apps/demos/scenery/scenes/ingame.c

@@ -179,6 +179,7 @@ static void draw_terrain(SceneIngame *scn) {
             draw_billboard("/assets/grasses/10.png",
                           (Vec3){ (float)x, d0 + 0.15f, (float)y },
                           (Vec2){0.3f, 0.3f},
+                          NULL,
                           (Color){255, 255, 255, 255}, true);
         }
     }

include/twn_draw.h

@@ -66,7 +66,6 @@ TWN_API void draw_triangle(char const *texture,
                            Color       c1,      /* optional, default: all 255 */
                            Color       c2);     /* optional, default: all 255 */
 
-/* TODO: double sided option */
 TWN_API void draw_quad(char const *texture,
                        Vec3        v0,          /* upper-left */
                        Vec3        v1,          /* bottom-left */
@@ -75,11 +74,12 @@ TWN_API void draw_quad(char const *texture,
                        Rect        texture_region,
                        Color       color);      /* optional, default: all 255 */
 
-TWN_API void draw_billboard(const char *texture,
+TWN_API void draw_billboard(char const *texture,
-                            Vec3 position,
+                            Vec3        position,
-                            Vec2 size,
+                            Vec2        size,
-                            Color color,        /* optional, default: all 255 */
+                            Rect const *texture_region, /* optional, default: NULL */
-                            bool cylindrical);  /* optional, default: false */
+                            Color       color,          /* optional, default: all 255 */
+                            bool        cylindrical);   /* optional, default: false */
 
 TWN_API void draw_camera_2d(Vec2 position,      /* optional, default: (0, 0) */
                             float rotation,     /* optional, default: 0 */

share/twn_api.json

@@ -180,6 +180,7 @@
                 { "name": "texture", "type": "char *" },
                 { "name": "position", "type": "Vec3" },
                 { "name": "size", "type": "Vec2" },
+                { "name": "texture_region", "type": "Rect *", "default": {} },
                 { "name": "color", "type": "Color", "default": { "r": 255, "g": 255, "b": 255, "a": 255 } },
                 { "name": "cylindrical", "type": "bool", "default": false }
             ]

src/rendering/twn_billboards.c

@@ -9,9 +9,10 @@
 #include <stb_ds.h>
 
 
-void draw_billboard(const char *texture,
+void draw_billboard(char const *texture,
                     Vec3 position,
                     Vec2 size,
+                    Rect const *texture_region,
                     Color color,
                     bool cylindrical)
 {
@@ -30,8 +31,12 @@ void draw_billboard(const char *texture,
         .cylindrical = cylindrical,
         .position = position,
         .size = size,
+        .texture_region_opt_set = texture_region != NULL,
     };
 
+    if (texture_region)
+        billboard.texture_region_opt = *texture_region;
+
     struct SpaceBillboard *billboards = (struct SpaceBillboard *)(void *)batch_p->value.primitives;
 
     arrpush(billboards, billboard);
@@ -81,10 +86,10 @@ void finally_draw_billboard_batch(struct MeshBatch const *batch,
     const float xr = srcrect.x / dims.w;
     const float yr = srcrect.y / dims.h;
 
-    const Vec2 uv0 = { xr,           yr      };
+    const Vec2 uv0c = { xr,           yr      };
-    const Vec2 uv1 = { xr,           yr + hr };
+    const Vec2 uv1c = { xr,           yr + hr };
-    const Vec2 uv2 = { xr + wr,      yr + hr };
+    const Vec2 uv2c = { xr + wr,      yr + hr };
-    const Vec2 uv3 = { xr + wr,      yr      };
+    const Vec2 uv3c = { xr + wr,      yr      };
 
     for (size_t batch_n = 0; batch_n <= (primitives_len - 1) / QUAD_ELEMENT_BUFFER_LENGTH; batch_n++) {
 
@@ -107,6 +112,20 @@ void finally_draw_billboard_batch(struct MeshBatch const *batch,
                 b = vec3_mul(right_minus_up, ((Vec3){billboard.size.x, billboard.size.y, billboard.size.x }));
             }
 
+            Vec2 uv0, uv1, uv2, uv3;
+            if (billboard.texture_region_opt_set) {
+                uv0 = (Vec2){ (srcrect.x + billboard.texture_region_opt.x) / dims.w,
+                              (srcrect.y + billboard.texture_region_opt.y) / dims.h };
+                uv1 = (Vec2){ (srcrect.x + billboard.texture_region_opt.x) / dims.w,
+                              (srcrect.y + billboard.texture_region_opt.y  + billboard.texture_region_opt.h) / dims.h };
+                uv2 = (Vec2){ (srcrect.x + billboard.texture_region_opt.x  + billboard.texture_region_opt.w) / dims.w,
+                              (srcrect.y + billboard.texture_region_opt.y  + billboard.texture_region_opt.h) / dims.h };
+                uv3 = (Vec2){ (srcrect.x + billboard.texture_region_opt.x  + billboard.texture_region_opt.w) / dims.w,
+                              (srcrect.y + billboard.texture_region_opt.y) / dims.h };
+            } else {
+                uv0 = uv0c; uv1 = uv1c; uv2 = uv2c; uv3 = uv3c;
+            }
+
             struct ElementIndexedBillboard const payload = {
                 /* flat shading is assumed, so we can skip setting the duplicates */
                 .c0 = billboard.color,

src/rendering/twn_draw_c.h

@@ -121,6 +121,8 @@ typedef struct SpaceBillboard {
     Vec3 position;
     Vec2 size;
     Color color;
+    m_option_list(
+        Rect, texture_region )
     // TextureKey texture; /* is assumed from other places */
     bool cylindrical;
 } SpaceBillboard;