feat: add rasterization primitives

src/core/raster.c

@@ -0,0 +1,80 @@
+#include "raster.h"
+#include "primitives.h"
+#include "stddef.h"
+
+void add_edge(EdgeBuffer *buffer, Edge edge) {
+  if (buffer->count >= buffer->capacity) {
+    buffer->capacity = buffer->capacity ? buffer->capacity * 2 : 4;
+    buffer->edges = realloc(buffer->edges, sizeof(Edge) * buffer->capacity);
+  }
+  buffer->edges[buffer->count++] = edge;
+}
+
+void flatten_line(EdgeBuffer *buffer, Line line) {
+  add_edge(buffer, (Edge){line.p1, line.p2, 0});
+}
+
+void flatten_polyline(EdgeBuffer *buffer, Polyline *line) {
+  for (size_t i = 0; i + 1 < line->count; i++) {
+    add_edge(buffer, (Edge){line->points[i], line->points[i + 1], 0});
+  }
+}
+
+void flatten_polygon(EdgeBuffer *buffer, Polygon *pg) {
+  size_t n = pg->count;
+  if (n < 3)
+    return;
+
+  for (size_t i = 0; i < n; i++) {
+    V2 p1 = pg->points[i];
+    V2 p2 = pg->points[(i + 1) % n];
+    int winding = (p1.y < p2.y) ? +1 : -1;
+    add_edge(buffer, (Edge){p1, p2, winding});
+  }
+}
+
+inline Framebuffer mk_framebuffer(unsigned int W, unsigned int H) {
+  Framebuffer fb = {.width = W, .height = H, .pixels = calloc(W * H * 3, 1)};
+  return fb;
+}
+
+inline void put_pixel(Framebuffer *fb, int x, int y, unsigned char r,
+                      unsigned char g, unsigned char b) {
+  if ((unsigned)x >= fb->width || (unsigned)y >= fb->height)
+    return;
+
+  int i = (y * fb->width + x) * 3;
+  fb->pixels[i + 0] = r;
+  fb->pixels[i + 1] = g;
+  fb->pixels[i + 2] = b;
+}
+
+void draw_line(Framebuffer *fb, V2 a, V2 b, unsigned char r, unsigned char g,
+               unsigned char bl) {
+  int x0 = (int)a.x;
+  int y0 = (int)a.y;
+  int x1 = (int)b.x;
+  int y1 = (int)b.y;
+
+  int dx = abs(x1 - x0);
+  int sx = x0 < x1 ? 1 : -1;
+  int dy = -abs(y1 - y0);
+  int sy = y0 < y1 ? 1 : -1;
+  int err = dx + dy;
+
+  for (;;) {
+    put_pixel(fb, x0, y0, r, g, bl);
+    if (x0 == x1 && y0 == y1)
+      break;
+
+    int e2 = 2 * err;
+    if (e2 >= dy) {
+      err += dy;
+      x0 += sx;
+    }
+    if (e2 <= dx) {
+      err += dx;
+      y0 += sy;
+    }
+  }
+}