Oversampling with 1 channel kinda works

main.c

@@ -206,6 +206,14 @@ static Window window;
 static GC default_gc;
 static XImage* xwindow_buffer;
 
+static int
+clamp_u32(u32 val, u32 cap) 
+{
+    u32 result = val;
+    if (val > cap) result = cap;
+    return(result);
+}
+
 static f32
 abs_f32(f32 v)
 {
@@ -438,38 +446,79 @@ render_glyph(struct glyph g, struct line_contour *lines,
 {
     int gwidth  = round_f32((g.xmax - g.xmin) * scale) + 1;
     int gheight = round_f32((g.ymax - g.ymin) * scale) + 1;
+    int oversample_y = 4;
+    f32 norm = 1.0f / (oversample_y + 1);
     
     struct intersection *intersections = malloc(lines->from[lines->ncontours] * sizeof(struct intersection));
     
     for (int y = 0; y < gheight && (at_y + y < height); ++y) {
-        u32 ncross = intersect_glyph(lines, y, intersections);
-        if (ncross) {
-            sort_intersections(intersections, ncross);
-            
-            int state = 0;
+        for (int yy = 1; yy <= oversample_y; ++yy) {
             
-            for (int i = 0; i < ncross - 1; ++i) {
-                struct intersection inter = intersections[i];
-                struct intersection next_inter = intersections[i + 1];
+            u32 ncross = intersect_glyph(lines, y + norm * yy, intersections);
+            if (ncross) {
+                sort_intersections(intersections, ncross);
                 
-                state += inter.dir;
+                int state = 0;
                 
-                if (state != 0) {
-                    f32 x0 = inter.x;
-                    f32 x1 = next_inter.x;
+                for (int i = 0; i < ncross - 1; ++i) {
+                    struct intersection inter = intersections[i];
+                    struct intersection next_inter = intersections[i + 1];
+                    
+                    state += inter.dir;
                     
-                    for (int x = x0; x < x1; ++x) {
-                        pixels[(y + at_y) * width + (at_x + x)] = 0x00;
+                    if (state != 0) {
+                        f32 x0 = inter.x;
+                        f32 x1 = next_inter.x;
+                        
+                        int x_from = x0;
+                        int x_to = x1;
+                        
+                        int start_enter = (state - inter.dir == 0);
+                        int end_enter = (state + next_inter.dir != 0);
+                        
+                        u32 start_brightness;
+                        u32 end_brightness;
+                        
+                        if (start_enter) {
+                            start_brightness = (x_from + 1 - x0) * (255.99f / oversample_y);
+                        } else {
+                            start_brightness = (x0 - x_from) * (255.99f / oversample_y);
+                        }
+                        
+                        if (end_enter) {
+                            end_brightness = (x_to + 1 - x1) * (255.99f / oversample_y);
+                        } else {
+                            end_brightness = (x1 - x_to) * (255.99f / oversample_y);
+                        }
+                        
+                        for (int x = x_from; x < x_to; ++x) {
+                            pixels[(y + at_y) * width + (at_x + x)] += 255.99f / oversample_y;
+                            pixels[(y + at_y) * width + (at_x + x)] = clamp_u32(pixels[(y + at_y) * width + (at_x + x)], 255);
+                        }
+                        
+                        u32 new_start_brightness = clamp_u32(pixels[(y + at_y) * width + (at_x + x_from)] + start_brightness, 255);
+                        u32 new_end_brightness = clamp_u32(pixels[(y + at_y) * width + (at_x + x_to)] + end_brightness, 255);
+                        
+                        pixels[(y + at_y) * width + (at_x + x_from)] = new_start_brightness;
+                        pixels[(y + at_y) * width + (at_x + x_to)] = new_end_brightness;
                     }
                 }
             }
         }
-        
-#if DEBUG_SHOW_POINTS
-        _D_render_glyph_points(g, scale, pixels, width, height);
-#endif
     }
     
+#if 0
+    for (int y = 0; y < height; ++y) {
+        for (int x = 0; x < width; ++x) {
+            if (pixels[y * width + x] <= 255) {
+                u32 brightness = 255 - pixels[y * width + x];
+                u32 white = 0xFF000000 | brightness << 16 | brightness << 8 | brightness;
+                pixels[y * width + x] = white;
+            }
+        }
+    }
+#endif
+    
     free(intersections);
 }
 
@@ -662,9 +711,9 @@ main(int argc, char **argv)
     
     
     for (;;) {
-        memset(pixels, 0xFFFFFFFF, width * height * 4);
+        memset(pixels, 0x00, width * height * 4);
         render_utf_string(font, 32, pixels, width, height, L"Привет, батя! Как поживаешь? Hello, Batya. Wazzaaap", 100, 100);
-        render_utf_string(font, 32, pixels, width, height, L"QQQQqqqqq", 100, 200);
+        render_utf_string(font, 20, pixels, width, height, L"QQQQqqqqq", 100, 200);
         
         XPutImage(display, window, default_gc, xwindow_buffer, 0, 0, 0, 0, width, height);