entity system!

src/game/shaders/frag.sc

@@ -1,8 +1,16 @@
 $input v_color0
+$input v_uv0
 
 #include "common.sh"
 
+float circle(vec2 uv, vec2 center, float size)
+{
+	vec2 relPos = uv - center;
+	vec2 distSq = relPos.x * relPos.x + relPos.y * relPos.y;
+	return sqrt(distSq) <= size ? 1.0 : 0.0;
+}
+
 void main()
 {
-	gl_FragColor = v_color0;
+	gl_FragColor = circle(v_uv0, vec2(0.5, 0.5), 0.5);
 }