wip: wgui backend

src/shaders/screen.frag

@@ -0,0 +1,17 @@
+#version 310 es
+precision highp float;
+
+layout (location = 0) in vec2 in_uv;
+layout (location = 0) out vec4 out_color;
+
+layout (set = 0, binding = 0) uniform sampler2D in_texture;
+layout (set = 1, binding = 0) uniform AlphaBlock {
+    uniform float alpha;
+};
+
+void main()
+{
+    out_color = texture(in_texture, in_uv);
+    out_color.a = alpha;
+}
+