fixed irritating bug in rendering that would miscalculate the tile bounds on occasion

Author: lowfatcode

examples/c/geometry.c

@@ -2,6 +2,7 @@
 #include "stb_image_write.h"
 
 #define PP_IMPLEMENTATION
+#define PP_DEBUG
 #include "pretty-poly.h"
 #include "helpers.h"
 
@@ -14,14 +15,25 @@ void set_pen(colour c) {
   pen = c;
 }
 
-void blend_tile(const pp_tile_t *t) {
-  for(int32_t y = t->y; y < t->y + t->h; y++) {
-    for(int32_t x = t->x; x < t->x + t->w; x++) {     
+void blend_tile(const pp_tile_t *t) {  
+  for(int y = t->y; y < t->y + t->h; y++) {
+    for(int x = t->x; x < t->x + t->w; x++) {     
       colour alpha_pen = pen;
       alpha_pen.a = alpha(pen.a, pp_tile_get(t, x, y));
       buffer[y][x] = blend(buffer[y][x], alpha_pen);
     }
   }
+
+  // draw border of tile for debugging
+  colour box = create_colour(160, 180, 200, 150);
+  for(int32_t x = t->x; x < t->x + t->w; x++) {     
+    buffer[t->y][x] = blend(buffer[t->y][x], box);
+    buffer[t->y + t->h][x] = blend(buffer[t->y + t->h][x], box);
+  }
+  for(int32_t y = t->y; y < t->y + t->h; y++) {
+    buffer[y][t->x] = blend(buffer[y][t->x], box);
+    buffer[y][t->x + t->w] = blend(buffer[y][t->x + t->w], box);
+  }
 }
 
 
@@ -35,7 +47,7 @@ int main() {
 
   for(int y = 0; y < HEIGHT; y++) {
     for(int x = 0; x < WIDTH; x++) {
-      buffer[x][y] = ((x / 8) + (y / 8)) % 2 == 0 ? create_colour(16, 32, 48, 255) : create_colour(0, 0, 0, 255);
+      buffer[y][x] = ((x / 8) + (y / 8)) % 2 == 0 ? create_colour(16, 32, 48, 255) : create_colour(0, 0, 0, 255);
     }
   }
 
@@ -47,8 +59,6 @@ int main() {
     {.points = hole,    .count = 4}
   };  
   pp_poly_t poly = {.paths = paths, .count = 2};
-  pp_render(&poly);
-
 
   for(int i = 0; i < 1000; i += 30) {
     pp_mat3_t t = pp_mat3_identity();

pretty-poly.h

@@ -145,7 +145,7 @@ pp_rect_t pp_polygon_bounds(pp_poly_t *p);
 
 #ifdef PP_IMPLEMENTATION
 
-pp_rect_t           _pp_clip = (pp_rect_t){0, 0, 320, 240};
+pp_rect_t           _pp_clip = (pp_rect_t){-INT_MAX, -INT_MAX, INT_MAX, INT_MAX};
 pp_tile_callback_t  _pp_tile_callback = NULL;
 pp_antialias_t      _pp_antialias = PP_AA_X4;
 pp_mat3_t          *_pp_transform = NULL;
@@ -424,10 +424,10 @@ int compare_nodes(const void* a, const void* b) {
 
 pp_rect_t render_nodes(pp_rect_t *tb) {
   pp_rect_t rb = {PP_TILE_BUFFER_SIZE << _pp_antialias, PP_TILE_BUFFER_SIZE << _pp_antialias, 0, 0}; // render bounds
-
+  int maxx = 0, minx = PP_TILE_BUFFER_SIZE << _pp_antialias;
   debug("  + render tile %d, %d - %d, %d\n", tb->x, tb->y, tb->w, tb->h);
 
-  for(uint32_t y = 0; y < ((uint32_t)PP_TILE_BUFFER_SIZE << _pp_antialias); y++) {
+  for(int y = 0; y < ((int)PP_TILE_BUFFER_SIZE << _pp_antialias); y++) {
 
     // debug("    : row %d node count %d\n", y, node_counts[y]);
 
@@ -437,7 +437,7 @@ pp_rect_t render_nodes(pp_rect_t *tb) {
 
     unsigned char* row_data = &tile_buffer[(y >> _pp_antialias) * PP_TILE_BUFFER_SIZE];
 
-    for(uint32_t i = 0; i < node_counts[y]; i += 2) {
+    for(int i = 0; i < node_counts[y]; i += 2) {
       int sx = nodes[y][i + 0];
       int ex = nodes[y][i + 1];
 
@@ -447,9 +447,10 @@ pp_rect_t render_nodes(pp_rect_t *tb) {
 
       // update render bounds
       rb.x = _pp_min(rb.x, sx);
-      rb.y = _pp_min(rb.y, y);
-      rb.w = _pp_max(rb.w, ex - rb.x);
-      rb.h = _pp_max(rb.h, y - rb.y + 1);
+      rb.y = _pp_min(rb.y, y);      
+      minx = _pp_min(_pp_min(sx, ex), minx);
+      maxx = _pp_max(_pp_max(sx, ex), maxx);
+      rb.h = y - rb.y + 1;
 
       //debug(" - render span at %d from %d to %d\n", y, sx, ex);
 
@@ -460,6 +461,8 @@ pp_rect_t render_nodes(pp_rect_t *tb) {
     }
   }
 
+  rb.w = maxx - minx;
+
   // shifting the width and height effectively "floors" the result which can
   // mean we lose a pixel off the right or bottom edge of the tile. by adding
   // either 1 (at x4) or 3 (at x16) we change that to a "ceil" instead ensuring
@@ -507,7 +510,7 @@ void pp_render(pp_poly_t *polygon) {
     polygon_bounds = pp_rect_transform(&polygon_bounds, _pp_transform);
   }
 
-  debug("  - bounds %d, %d (%d x %d)\n", polygon_bounds.x, polygon_bounds.y, polygon_bounds.w, polygon_bounds.h);
+  debug("  - polygon bounds %d, %d (%d x %d)\n", polygon_bounds.x, polygon_bounds.y, polygon_bounds.w, polygon_bounds.h);
   debug("  - clip %d, %d (%d x %d)\n", _pp_clip.x, _pp_clip.y, _pp_clip.w, _pp_clip.h);
 
 #ifdef USE_RP2040_INTERP