billboards!

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);
 }