feat: add round titlebars (#26)

sway/desktop/shaders/quad_round_tl.frag

@@ -0,0 +1,14 @@
+precision mediump float;
+varying vec4 v_color;
+varying vec2 v_texcoord;
+
+uniform vec2 size;
+uniform vec2 position;
+uniform float radius;
+
+void main() {
+    vec2 q = abs(gl_FragCoord.xy - position - size) - size + radius;
+   float distance = min(max(q.x,q.y),0.0) + length(max(q,0.0)) - radius;
+    float smoothedAlpha = 1.0 - smoothstep(-1.0, 0.5, distance);
+    gl_FragColor = mix(vec4(0), v_color, smoothedAlpha);
+}