Handle bgra layers

Shaders/painter/layer_copy_bgra.frag.glsl

@@ -0,0 +1,8 @@
+#version 330
+uniform sampler2D tex;
+in vec2 texCoord;
+in vec4 color;
+out vec4 FragColor;
+void main() {
+	FragColor = textureLod(tex, texCoord, 0).bgra * color;
+}