update

assets/shaders/2d-solid.fragment.glsl

@@ -1,8 +1,55 @@
 #version 330 core
-out vec4 frag_color;
+out vec4 pixel_color;
 
-in vec4 fragment_color;
+in vec4 frag_color;
+in vec2 frag_dest_position;
+in vec2 frag_dest_center;
+in vec2 frag_dest_half_size;
+in float frag_softness;
+in float frag_border_radius;
+in float frag_border_thickness;
+
+float roundedRectSDF(vec2 sample_pos, vec2 rect_center, vec2 rect_half_size, float r) {
+  vec2 d2 = (abs(rect_center - sample_pos) - rect_half_size + vec2(r, r));
+  return min(max(d2.x, d2.y), 0.0) + length(max(d2, 0.0)) - r;
+}
 
 void main() {
-    frag_color = fragment_color;
+    vec2 softness_padding = vec2(
+        max(0, frag_softness*2-1), 
+        max(0, frag_softness*2-1));
+
+    float border_factor = 1.0f;
+    if (frag_border_thickness != 0) {
+        vec2 interior_half_size = frag_dest_half_size - vec2(frag_border_thickness);
+
+        float interior_radius_reduce_f = min(
+            interior_half_size.x / frag_dest_half_size.x,
+            interior_half_size.y / frag_dest_half_size.y);
+
+        float interior_corner_radius = frag_border_radius * interior_radius_reduce_f * interior_radius_reduce_f;
+
+        float inside_d = roundedRectSDF(
+            frag_dest_position, 
+            frag_dest_center, 
+            interior_half_size - softness_padding, 
+            interior_corner_radius);
+
+
+        float inside_f = smoothstep(0, 2*frag_softness, inside_d);
+        border_factor = inside_f;
+    }
+
+    float dist = roundedRectSDF(
+        frag_dest_position, 
+        frag_dest_center, 
+        frag_dest_half_size - softness_padding, 
+        frag_border_radius);
+
+    // For texturing later
+    float sample = 1;
+
+    float sdf_factor = 1.0f - smoothstep(0, 2*frag_softness, dist);
+
+    pixel_color = frag_color * sample * sdf_factor * border_factor;
 };