Sign in to follow this  
Gazoo

OpenGL More FBO and buffer questions...

Recommended Posts

Gazoo    122
Hello again, I hope people will indulge me in my idiocy a bit longer on this forum as I'm having a bit of trouble getting the "OpenGL Frame Buffer Object 101" to work properly... Basically I'm trying to render the images to a depth buffer in the hopes of achieving a higher color resolution. I read somewhere that pixels rendered to the color buffer are all clamped and to 0-255 values where as the same is not true for example the depth buffer...? Perhaps I am wrong in this assumption? Anyways - I am hoping someone has the time to glance at some of my code and see if they can spot anything out of order... Just to get something out of of the way - If I do NOT render to the FBO object - i.e call "" before rendering, I get a pretty blue/white rotating wierd triangle. Some initialization code
gpuAiVertexProgram = cgCreateProgramFromFile(gpuAiContext,
						CG_SOURCE,
						"testShader.cg",
						gpuAiVertexProfile,
						"main",
						NULL);

if(gpuAiVertexProgram != NULL)
{
	/* Vertex shader only needs to be loaded once */
	cgGLLoadProgram(gpuAiVertexProgram);

	/* Bind parameters to give access to variables in the shader */
	//KdParam = cgGetNamedParameter(VertexProgram, "Kd");
	ModelViewProjParam = cgGetNamedParameter(gpuAiVertexProgram, "ModelViewProj");
	ModelViewProjITParam = cgGetNamedParameter(gpuAiVertexProgram, "ModelViewProjIT");
	//VertexColorParam = cgGetNamedParameter(VertexProgram, "IN.VertexColor");
}

// Generate Frame buffer so we can use it!
glGenFramebuffersEXT(1, &fbo);							// Get a handle
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);			// GL_FRAMEBUFFER_EXT is apparently the only bindable destination right now.
		
// Generate a Renderbuffer for the FBO
glGenRenderbuffersEXT(1, &depthbuffer);				// Get a handle
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, 512, 512);	// Define storage space for the renderbuffer

// Generate a texture
glGenTextures(1, &img);
glBindTexture(GL_TEXTURE_2D, img);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8,  512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

// Attach function FBO<->Renderbuffer
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthbuffer);

// Attach function FBO<->Texture
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, img, 0);

if (checkFramebufferStatus()) {
	printf("Successfully attached FBO to Depthbuffer! \n");
} else {
	exit(-3);
}

The display code...
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glPushMatrix();
glRotatef(angle,0.0,1.0,0.0);

if (enableCG) {
	cgGLBindProgram(gpuAiVertexProgram);

	if(ModelViewProjParam != NULL)
		cgGLSetStateMatrixParameter(ModelViewProjParam,						CG_GL_MODELVIEW_PROJECTION_MATRIX,
		CG_GL_MATRIX_IDENTITY);

	if(ModelViewProjITParam != NULL)
		cgGLSetStateMatrixParameter(ModelViewProjITParam,
		CG_GL_MODELVIEW_MATRIX,
		CG_GL_MATRIX_INVERSE_TRANSPOSE);

	cgGLEnableProfile(gpuAiVertexProfile);
}

glPushAttrib(GL_VIEWPORT_BIT);
glViewport(0,0,512, 512);

glBegin(GL_TRIANGLE_STRIP);
{
	glVertex3f(-0.8,-0.8,0.0);
	glVertex3f(0.8,-0.8,0.0);
	glVertex3f(0.0,0.8,0.0);
	//glVertex3f(-0.8f, 0.8f, -114.0f);
	//glVertex3f(-0.7f, 0.8f, -114.0f);

	//glVertex3f(-0.75f, 0.9f, -114.0f);

	glVertex3f(-0.65f, 0.9f, 2.0f);
	//glVertex3f(-0.6f, 0.8f, -114.0f);
}
glEnd();

glPopAttrib();

if (enableCG) {
	cgGLDisableProfile(gpuAiVertexProfile);
}

glPopMatrix();
		
// swapping the buffers causes the rendering above to be 
// shown
glutSwapBuffers();
		
// finally increase the angle for the next frame
angle++;

glFlush();

I'm using imdebug (which is a small tool to read an image into an extra tool and then look closer at it) to peer into the various buffers and have a look at whats inside. Here are the calls I use... The odd thing is... If I use imdebug to read from the screen it works fine when I render to it, but also when rendering to the depth buffer is active (or should be) - only then I see the blue triangle basically overwriting itself creating lots of layers of itself... Hmmm perhaps that needs clarification...
switch(key) {
	case GLUT_KEY_F1 :
		if (enableCG) {
			enableCG = false;
			printf("Cg Disabled...\n");
		} else {
			enableCG = true;
			printf("Cg Enabled...\n");
		}
		break;
	case GLUT_KEY_F2 :
		if (rendertoBF) {
			rendertoBF = false;
			glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
		} else {
			rendertoBF = true;
			glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);
		}
		break;
	case GLUT_KEY_F3 :
		// Try to use imdebug to display whats in the texture attached to the depthbuffer
		imdebug("rgba  w=%d h=%d %p", 512, 512, &img);
		break;
	case GLUT_KEY_F4 :
		// Try to use imdebug to render directly from the depth buffer
		imdebugDepth(0,0,512,512);
		break;
	case GLUT_KEY_F5 :
		printf("Read pixel from screen (color buffer?) into imdebug");
		imdebugPixels(0,0,512,512,GL_RGBA);
		break;
}

Any and all answers are much appreciated! Regards, Gazoo

Share this post


Link to post
Share on other sites
MARS_999    1627
If you don't want your colors to be clamped to 0-1 you need to use floating point buffer format. But if you use a floating point texture render target and render that texture you should be able to get around it that way since the data should be saved outside the 0-1 limit.

Share this post


Link to post
Share on other sites
Gazoo    122
Ok - so technically it should be possible to get some values that are not clamped... That's at least encouraging... Now if only I could figure out why my program crashes when I try to read the texture using the above code...

Regards,

Gazoo

Share this post


Link to post
Share on other sites
Gazoo    122
Well - the reason for the program crashing was of course my own doing. I provided imdebug with an OpenGL pointer to the texture and not a pointer to local memory where an array filled with "pixels" awaited. As a result it read the openGL pointer and kept going into memory that it wasn't allowed to read, which lead to a crash...

I still haven't figured out why reading directly from the depth buffer gives me a completely white image...

Regards,

Gazoo

Share this post


Link to post
Share on other sites
_the_phantom_    11250
Depth buffer values are indeed clamped, but into a [0,1] range as a floating point value (16 or 24bit depending on hardware and requested depth). If you want unclampped data outside of the [0,1] range then you need to use floating point textures or render targets as render targets for the FBO.

Share this post


Link to post
Share on other sites
Gazoo    122
Hey,

Thanks for the replies... One further question thou... In the "OpenGL Frame Buffer Object 101" tutorial, you start off with attaching a depthbuffer to the FBO... I have messed around with the code a bit and I am lead to believe that that the depthbuffer doesn't really influence or affect the rendering to a texture by use of the same FBO.

Is this correct? I assume the depth buffer is only in the tutorial in order to show that it is possible to use the FBO to render into an existing buffer instead of a texture?

Regards,

Gazoo

Share this post


Link to post
Share on other sites
_the_phantom_    11250
Nope, the depth buffer is attached so that you can do depth culling on objects rendered to the FBO just as you would when rendering to the normal colour buffer when drawing.

So, it does affect what appears in the texture during the render, much how it affects what appears in the main framebuffer when you render 'normally'.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Partner Spotlight

  • Similar Content

    • By pseudomarvin
      I assumed that if a shader is computationally expensive then the execution is just slower. But running the following GLSL FS instead just crashes
      void main() { float x = 0; float y = 0; int sum = 0; for (float x = 0; x < 10; x += 0.00005) { for (float y = 0; y < 10; y += 0.00005) { sum++; } } fragColor = vec4(1, 1, 1 , 1.0); } with unhandled exception in nvoglv32.dll. Are there any hard limits on the number of steps/time that a shader can take before it is shut down? I was thinking about implementing some time intensive computation in shaders where it would take on the order of seconds to compute a frame, is that possible? Thanks.
    • By Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
       
      Thanks
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
  • Popular Now