Migrate the borders program

kitty/border_vertex.glsl

@@ -1,7 +1,7 @@
 #version GLSL_VERSION
-uniform vec3 colors[3];
 uniform uvec2 viewport;
 in uvec4 rect;  // left, top, right, bottom
+in uint rect_color;
 out vec3 color;
 
 // indices into the rect vector
@@ -17,10 +17,16 @@ const uvec2 pos_map[] = uvec2[4](
     uvec2(LEFT, TOP)   
 );
 
-float to_opengl(uint val, uint sz) { return -1.0 + 2.0 * (float(val) / float(sz)); }
+float to_opengl(uint val, uint sz) {
+    return -1.0 + 2.0 * (float(val) / float(sz)); 
+}
+
+float to_color(uint c) {
+    return float(c & uint(0xff)) / 255.0;
+}
 
 void main() {
     uvec2 pos = pos_map[gl_VertexID];
     gl_Position = vec4(to_opengl(rect[pos.x], viewport.x), to_opengl(rect[pos.y], viewport.y), 0, 1);
-    color = vec3(1, 0, 0);
+    color = vec3(to_color(rect_color >> 16), to_color(rect_color >> 8), to_color(rect_color));
 }