Implement simple overlay effect that fills a texture over a render target

libs/gfx/include/psemek/gfx/effect/overlay.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <psemek/gfx/texture.hpp>
+#include <psemek/gfx/render_target.hpp>
+
+#include <psemek/util/pimpl.hpp>
+
+namespace psemek::gfx
+{
+
+	struct overlay
+	{
+		overlay();
+		~overlay();
+
+		void invoke(texture_2d const & src, render_target const & dst);
+
+	private:
+		psemek_declare_pimpl
+	};
+
+}

libs/gfx/source/effect/overlay.cpp

@@ -0,0 +1,75 @@
+#include <psemek/gfx/effect/overlay.hpp>
+#include <psemek/gfx/program.hpp>
+#include <psemek/gfx/array.hpp>
+
+#include <psemek/util/pimpl.hpp>
+
+namespace psemek::gfx
+{
+
+	static char const overlay_vs[] =
+R"(#version 330
+
+const vec4 vertices[6] = vec4[6](
+	vec4(-1.0, -1.0, 0.0, 1.0),
+	vec4( 1.0, -1.0, 0.0, 1.0),
+	vec4( 1.0,  1.0, 0.0, 1.0),
+
+	vec4(-1.0, -1.0, 0.0, 1.0),
+	vec4( 1.0,  1.0, 0.0, 1.0),
+	vec4(-1.0,  1.0, 0.0, 1.0)
+);
+
+out vec2 texcoord;
+
+void main()
+{
+	gl_Position = vertices[gl_VertexID];
+	texcoord = vertices[gl_VertexID].xy * 0.5 + vec2(0.5);
+}
+)";
+
+	static char const overlay_fs[] =
+R"(#version 330
+
+uniform sampler2D u_texture;
+
+in vec2 texcoord;
+
+out vec4 out_color;
+
+void main()
+{
+	out_color = texture(u_texture, texcoord);
+}
+)";
+
+	struct overlay::impl
+	{
+		gfx::program program{overlay_vs, overlay_fs};
+		gfx::array array;
+	};
+
+	overlay::overlay()
+		: pimpl_{std::make_unique<struct impl>()}
+	{
+		impl().program.bind();
+		impl().program["u_texture"] = 0;
+	}
+
+	overlay::~overlay() = default;
+
+	void overlay::invoke(texture_2d const & src, render_target const & dst)
+	{
+		gl::Disable(gl::DEPTH_TEST);
+		gl::Disable(gl::CULL_FACE);
+
+		dst.bind();
+		gl::ActiveTexture(gl::TEXTURE0);
+		src.bind();
+		impl().array.bind();
+		impl().program.bind();
+		gl::DrawArrays(gl::TRIANGLES, 0, 6);
+	}
+
+}