rendering: use sprite batching techniques for rect primitives, unite their render path

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);
+}