rendering to a frame buffer (but not yet drawing it again)

data/shaders/fs_simple.glsl

@@ -1,6 +1,6 @@
 #version 330 core
 
-out vec3 color;
+layout(location = 0) out vec3 color;
 
 void main() {
 	color = vec3(1, 0, 0);

src/modules/RenderModule.cc

@@ -122,12 +122,24 @@ glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data
 	mProgram = RenderProgram("data/shaders/vs_simple.glsl", "data/shaders/fs_simple.glsl");
 	bool load_result = mProgram.Load();
 	assert(load_result);
+
+	mRenderTarget = RenderTarget (width, height, RenderTarget::EnableColor | RenderTarget::EnableDepth);
 }
 
 void Renderer::Shutdown() {
 	glDeleteVertexArrays(1, &mMesh.mVertexArrayId);
 }
 void Renderer::RenderGl() {
+	// enable the render target
+	glBindFramebuffer(GL_FRAMEBUFFER, mRenderTarget.mFrameBufferId);
+	GLenum DrawBuffers[1] = { GL_COLOR_ATTACHMENT0 };
+	glDrawBuffers(1, DrawBuffers);
+
+	if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+		gLog ("Cannot render: frame buffer invalid!");
+	}
+
+	// clear color and depth
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
 	glUseProgram(mProgram.mProgramId);

src/modules/RenderModule.h

@@ -114,6 +114,7 @@ struct Renderer {
 	std::vector<Camera> cameras;
 	Mesh mMesh;
 	RenderProgram mProgram;
+	RenderTarget mRenderTarget;
 
 	Renderer() :
 		initialized(false),

src/modules/RenderUtils.cc

@@ -10,6 +10,10 @@
 
 using namespace SimpleMath;
 
+//
+// RenderProgram
+//
+
 RenderProgram::~RenderProgram() {
 	if (mProgramId > 0)
 		glDeleteProgram(mProgramId);
@@ -109,4 +113,35 @@ bool RenderProgram::Load() {
 	return true;
 }
 
+//
+// RenderTarget
+//
+RenderTarget::RenderTarget(int width, int height, int flags) {
+	glGenFramebuffers(1, &mFrameBufferId);
+	glBindFramebuffer(GL_FRAMEBUFFER, mFrameBufferId);
+
+	if (flags & EnableColor) {
+		glGenTextures(1, &mColorTexture);
+		glBindTexture(GL_TEXTURE_2D, mColorTexture);
+
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, 0);
+
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+
+		glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, mColorTexture, 0);
+	}
+
+	if (flags & EnableDepth) {
+		glGenRenderbuffers(1, &mDepthBuffer);
+		glBindRenderbuffer(GL_RENDERBUFFER, mDepthBuffer);
+		glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);
+		glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, mDepthBuffer);
+	}
+}
+
+RenderTarget::~RenderTarget() {
+	// TODO: cleanup
+}
+
 

src/modules/RenderUtils.h

@@ -144,5 +144,19 @@ struct RenderProgram {
 	bool Load();
 };
 
+struct RenderTarget {
+	GLuint mFrameBufferId = -1;
+	GLuint mColorTexture = -1;
+	GLuint mDepthBuffer = -1;
+
+	typedef enum {
+		EnableColor = 1,
+		EnableDepth = 2
+	} Flags;
+
+	RenderTarget() {};
+	RenderTarget(int width, int height, int flags);
+	~RenderTarget();
+};
 
 #endif