refactor ImGUI code files

internal/igwrap/backend/shader.frag

@@ -0,0 +1,33 @@
+#version 330
+
+#define FLAG_RED    (1<<0)
+#define FLAG_GREEN  (1<<1)
+#define FLAG_BLUE   (1<<2)
+#define FLAG_ALPHA  (1<<3)
+#define FLAG_COLORS (FLAG_RED | FLAG_GREEN | FLAG_BLUE | FLAG_ALPHA)
+
+#define FLAG_LINEAR (1<<4)
+
+uniform sampler2D tex;
+uniform int flags;
+
+in vec2 fragUV;
+in vec4 fragColor;
+
+out vec4 outputColor;
+
+const float gamma = 2.2;
+
+void main() {
+	if ((flags & FLAG_COLORS) == FLAG_RED) {
+		outputColor = vec4(fragColor.rgb, fragColor.a * texture(tex, fragUV.st).r);
+	} else {
+		vec4 color = texture(tex, fragUV.st);
+		if ((flags & FLAG_LINEAR) != 0)
+			color.rgb = pow(color.rgb, vec3(1.0/gamma));
+		outputColor = color * fragColor;
+		if ((flags & FLAG_ALPHA) == 0)
+			outputColor.a = 1;
+	}
+}
+