triangle

2 files changed, 205 insertions, 4 deletions

diff --git a/examples/triangle.c b/examples/triangle.c
new file mode 100644
index 0000000..452dc94
--- /dev/null
+++ b/examples/triangle.c
@@ -0,0 +1,23 @@
+#include <math.h>
+
+#include "../sponge.h"
+
+#define SPEED (4)
+static int32_t offset = 0;
+
+void init() {}
+
+void draw_frame(sponge_Texture c) {
+    sponge_clear(c, 0xFF000000);
+    offset += SPEED;
+
+    if (offset > 100)
+        offset = -100;
+
+    sponge_draw_triangle_col3(
+        c,
+        30, 30 + offset,
+        c.width - 30, 50 + offset,
+        30, c.height - 30 + offset,
+        0xFFFF0000, 0xFF00FF00, 0xFF0000FF);
+}
diff --git a/sponge.h b/sponge.h
index 89d3c9f..1c13a9c 100644
--- a/sponge.h
+++ b/sponge.h
@@ -7,10 +7,23 @@ typedef struct {
     uint32_t stride;
 } sponge_Texture;
 
-int  sponge_canvas_valid(sponge_Texture c);
-void sponge_clear       (sponge_Texture c, uint32_t color);
-void sponge_draw_rect   (sponge_Texture c, uint32_t x0, uint32_t y0, uint32_t x1, uint32_t y1, uint32_t color);
-void sponge_draw_texture(sponge_Texture c, uint32_t x0, uint32_t y0, sponge_Texture tex);
+typedef struct {
+    float x;
+    float y;
+} sponge_Vec2;
+
+sponge_Vec2 sponge_add2(sponge_Vec2 v0, sponge_Vec2 v1);
+sponge_Vec2 sponge_sub2(sponge_Vec2 v0, sponge_Vec2 v1);
+float       sponge_dot2(sponge_Vec2 v0, sponge_Vec2 v1);
+
+int  sponge_canvas_valid      (sponge_Texture c);
+void sponge_clear             (sponge_Texture c, uint32_t color);
+void sponge_draw_rect         (sponge_Texture c, uint32_t x0, uint32_t y0, uint32_t x1, uint32_t y1, uint32_t color);
+void sponge_draw_texture      (sponge_Texture c, uint32_t x0, uint32_t y0, sponge_Texture tex);
+void sponge_draw_triangle_col (sponge_Texture c, int32_t x0, int32_t y0, int32_t x1, int32_t y1, int32_t x2, int32_t y2, uint32_t color);
+void sponge_draw_triangle_col3(
+    sponge_Texture c, int32_t x0, int32_t y0, int32_t x1, int32_t y1, int32_t x2, int32_t y2,
+    uint32_t color0, uint32_t color1, uint32_t color2);
 
 // TODO(kard): prefix stripping
 
@@ -22,6 +35,116 @@ void sponge_draw_texture(sponge_Texture c, uint32_t x0, uint32_t y0, sponge_Text
 #define SPONGE_ASSERT(x) assert(x)
 #endif // SPONGE_ASSERT
 
+#define SPONGE__CLAMP(val, min, max) ((val) < (min) ? (min) : ((val) > (max) ? (max) : (val)))
+#define SPONGE__MIN(x, y) ((x) < (y) ? (x) : (y))
+#define SPONGE__MAX(x, y) ((x) > (y) ? (x) : (y))
+
+// TODO(kard): these color functions will probably be public in the future
+
+void sponge__col_unpack(uint32_t col, uint32_t *a, uint32_t *r, uint32_t *g, uint32_t *b) {
+    *b = col & 0xFF;
+    col = col >> 8;
+    *g = col & 0xFF;
+    col = col >> 8;
+    *r = col & 0xFF;
+    col = col >> 8;
+    *a = col & 0xFF;
+}
+
+uint32_t sponge__col_pack(uint32_t a, uint32_t r, uint32_t g, uint32_t b) {
+    uint32_t result = 0;
+    result |= SPONGE__CLAMP(a, 0x00, 0xFF);
+    result = result << 8;
+    result |= SPONGE__CLAMP(r, 0x00, 0xFF);
+    result = result << 8;
+    result |= SPONGE__CLAMP(g, 0x00, 0xFF);
+    result = result << 8;
+    result |= SPONGE__CLAMP(b, 0x00, 0xFF);
+    return result;
+}
+
+uint32_t sponge__col_add(uint32_t col0, uint32_t col1) {
+    uint32_t a0, r0, g0, b0;
+    uint32_t a1, r1, g1, b1;
+    sponge__col_unpack(col0, &a0, &r0, &g0, &b0);
+    sponge__col_unpack(col1, &a1, &r1, &g1, &b1);
+    uint32_t a = a0 + a1;
+    uint32_t r = r0 + r1;
+    uint32_t g = g0 + g1;
+    uint32_t b = b0 + b1;
+    return sponge__col_pack(a, r, g, b);
+}
+
+uint32_t sponge__col_mul(uint32_t col, float t) {
+    float b = (float)(col & 0xFF) * t;
+    col = col >> 8;
+    float g = (float)(col & 0xFF) * t;
+    col = col >> 8;
+    float r = (float)(col & 0xFF) * t;
+    col = col >> 8;
+    float a = (float)(col & 0xFF) * t;
+
+    return sponge__col_pack((uint32_t)a, (uint32_t)r, (uint32_t)g, (uint32_t)b);
+}
+
+typedef struct {
+    sponge_Vec2 v0;
+    sponge_Vec2 v1;
+    float d00;
+    float d01;
+    float d11;
+    float denom;
+} sponge_BarycentricContext;
+
+// TODO(kard): measure if caching this makes sense
+sponge_BarycentricContext sponge__barycentric_init(sponge_Vec2 t0, sponge_Vec2 t1, sponge_Vec2 t2) {
+    sponge_BarycentricContext result;
+    result.v0 = sponge_sub2(t1, t0);
+    result.v1 = sponge_sub2(t2, t0);
+    result.d00 = sponge_dot2(result.v0, result.v0);
+    result.d01 = sponge_dot2(result.v0, result.v1);
+    result.d11 = sponge_dot2(result.v1, result.v1);
+    result.denom = (result.d00 * result.d11) - (result.d01 * result.d01);
+    return result;
+}
+
+void sponge__barycentric(
+    sponge_BarycentricContext ctx, sponge_Vec2 p,
+    sponge_Vec2 t0,
+    sponge_Vec2 t1,
+    sponge_Vec2 t2,
+    float *u, float *v, float *w
+) {
+    sponge_Vec2 v2 = sponge_sub2(p, t0);
+    float d20 = sponge_dot2(v2, ctx.v0);
+    float d21 = sponge_dot2(v2, ctx.v1);
+    float vr = (ctx.d11 * d20 - ctx.d01 * d21) / ctx.denom;
+    float wr = (ctx.d00 * d21 - ctx.d01 * d20) / ctx.denom;
+    float ur = 1.0f - vr - wr;
+    *u = ur;
+    *v = vr;
+    *w = wr;
+}
+
+
+sponge_Vec2 sponge_add2(sponge_Vec2 v0, sponge_Vec2 v1) {
+    sponge_Vec2 result;
+    result.x = v0.x + v1.x;
+    result.y = v0.y + v1.y;
+    return result;
+}
+
+sponge_Vec2 sponge_sub2(sponge_Vec2 v0, sponge_Vec2 v1) {
+    sponge_Vec2 result;
+    result.x = v0.x - v1.x;
+    result.y = v0.y - v1.y;
+    return result;
+}
+
+float sponge_dot2(sponge_Vec2 v0, sponge_Vec2 v1) {
+    return (v0.x * v1.x) + (v0.y * v1.y);
+}
+
 int sponge_canvas_valid(sponge_Texture c) {
     return c.width != 0 && c.height != 0;
 }
@@ -67,5 +190,60 @@ void sponge_draw_texture(sponge_Texture c, uint32_t x0, uint32_t y0, sponge_Text
     }
 }
 
+void sponge_draw_triangle_col(sponge_Texture c, int32_t x0, int32_t y0, int32_t x1, int32_t y1, int32_t x2, int32_t y2, uint32_t color) {
+    sponge_draw_triangle_col3(c, x0, y0, x1, y1, x2, y2, color, color, color);
+}
+
+// NOTE(kard):
+// this does not accept floats on purpose.
+// there are more efficient algorithms for producing triangle pixels other than
+// checking every one of them in rectangle with barycentric coords (e.g. using Brehensam algorithm)
+// and they can work with integer coordinates.
+// TODO(kard): this should be explored in the future
+// TODO(kard): backface culling?
+void sponge_draw_triangle_col3(
+    sponge_Texture c, int32_t x0, int32_t y0, int32_t x1, int32_t y1, int32_t x2, int32_t y2,
+    uint32_t color0, uint32_t color1, uint32_t color2) {
+    SPONGE_ASSERT(sponge_canvas_valid(c));
+
+    sponge_Vec2 t0 = { .x = (float)x0, .y = (float)y0 };
+    sponge_Vec2 t1 = { .x = (float)x1, .y = (float)y1 };
+    sponge_Vec2 t2 = { .x = (float)x2, .y = (float)y2 };
+
+    int32_t smin_x = SPONGE__MIN(x0, SPONGE__MIN(x1, x2));
+    int32_t smax_x = SPONGE__MAX(x0, SPONGE__MAX(x1, x2));
+    int32_t smin_y = SPONGE__MIN(y0, SPONGE__MIN(y1, y2));
+    int32_t smax_y = SPONGE__MAX(y0, SPONGE__MAX(y1, y2));
+
+    uint32_t min_x = (uint32_t)SPONGE__CLAMP(smin_x, 0, (int32_t)(c.width - 1));
+    uint32_t max_x = (uint32_t)SPONGE__CLAMP(smax_x, 0, (int32_t)(c.width - 1));
+    uint32_t min_y = (uint32_t)SPONGE__CLAMP(smin_y, 0, (int32_t)(c.height - 1));
+    uint32_t max_y = (uint32_t)SPONGE__CLAMP(smax_y, 0, (int32_t)(c.height - 1));
+
+    sponge_BarycentricContext ctx = sponge__barycentric_init(t0, t1, t2);
+
+    uint32_t *row = c.pixels + (min_y * c.stride);
+
+    for (uint32_t y = min_y; y <= max_y; y++, row += c.stride) {
+        for (uint32_t x = x0; x <= max_x; x++) {
+            float u, v, w;
+            sponge_Vec2 p = { .x = (float)x, .y = (float)y };
+            sponge__barycentric(ctx, p, t0, t1, t2, &u, &v, &w);
+            if (u > 0.0f && v > 0.0f && w > 0.0f)
+            {
+                // TODO(kard): make more robust, this probably has a lot of off by 1 errors
+                uint32_t c0 = sponge__col_mul(color0, u);
+                uint32_t c1 = sponge__col_mul(color1, v);
+                uint32_t c2 = sponge__col_mul(color2, w);
+                uint32_t result = 0;
+                result = sponge__col_add(result, c0);
+                result = sponge__col_add(result, c1);
+                result = sponge__col_add(result, c2);
+                row[x] = result;
+            }
+        }
+    }
+}
+
 #endif // SPONGE_IMPLEMENTATION