rounded quads baby!

resources/shaders/source/rect.frag.glsl

@@ -1,9 +1,55 @@
 #version 450
 
-layout(location = 0) in vec4 col;
+layout(location = 0) in vec4 color;
+layout(location = 1) in vec2 local_position;
+layout(location = 2) in vec2 global_position;
+layout(location = 3) in float radius;
+
 layout(location = 0) out vec4 fragColor;
 
+// SDF for a rounded rectangle given the centerpoint, half size and radius, all in pixels
+float sdf_rr(vec2 p, vec2 center, vec2 half_size, float radius) {
+    // Translate fragment position to rectangle's coordinate system
+    p -= center;
+    // Adjust for rounded corners: shrink the rectangle by the radius
+    vec2 q = abs(p) - half_size + radius;
+    // Combine distance components:
+    // - max(q, 0.0) handles regions outside the rounded corners
+    // - min(max(q.x, q.y), 0.0) handles regions inside the rectangle
+    return length(max(q, 0.0)) + min(max(q.x, q.y), 0.0) - radius;
+}
+
 void main()
 {
-	fragColor = col;
+    // local_position are normalized coordinates in the rectangle, passed from the
+    // vertex shader
+    /*
+     * Window
+     * +-----------------------+
+     * |              (1,1)    |
+     * |     +----------x      |
+     * |     |          |      |
+     * |     |          |      |
+     * |     |   Rect   |      |
+     * |     |          |      |
+     * |     |          |      |
+     * |     x----------+      |
+     * |  (-1,-1)              |
+     * |                       |
+     * +-----------------------+
+     */ 
+
+    vec2 dx = dFdx(local_position);
+    vec2 dy = dFdy(local_position);
+    // Conversion from normalized coordinates to pixels
+    vec2 norm_to_px = 1.0 / vec2(length(dx), length(dy));
+	
+    vec2 centerpoint = global_position - local_position * norm_to_px;
+    // the half size of the rectangle is also norm_to_px
+    vec2 half_size = 1.0 * norm_to_px;
+
+    float distance = sdf_rr(global_position, centerpoint, half_size, radius);
+    float alpha = 1.0 - smoothstep(0.0, 1.0, max(distance, 0.0));
+
+	fragColor = vec4(color.rgb, color.a * alpha);
 }

resources/shaders/source/rect.vert.glsl

@@ -10,6 +10,9 @@ layout(location = 1) in ivec2 uv;
 layout(location = 2) in ivec4 color;
 
 layout(location = 0) out vec4 col;
+layout(location = 1) out vec2 local_position;
+layout(location = 2) out vec2 global_position;
+layout(location = 3) out float radius;
 
 void main()
 {
@@ -24,5 +27,10 @@ void main()
 	pos.y = -(float(position.y)*2.0 / view.y - 1.0);
 
 	gl_Position = vec4(pos+shift, 0.0, 1.0);
+
+	local_position = vec2(sign(uv));
+	global_position = gl_Position.xy;
+	radius = abs(float(uv.x));
+	
 	col = vec4(color) / 255.0;
 }