compositor: Support alpha for solid color surfaces
diff --git a/src/compositor.c b/src/compositor.c
index f9e1f23..60142d1 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -2156,9 +2156,10 @@
 static const char solid_fragment_shader[] =
 	"precision mediump float;\n"
 	"uniform vec4 color;\n"
+	"uniform float alpha;\n"
 	"void main()\n"
 	"{\n"
-	"   gl_FragColor = color\n;"
+	"   gl_FragColor = alpha * color\n;"
 	"}\n";
 
 static int