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Garret

OpenGL Using Frame Buffer

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Hi, I've got a problem when trying to create subj in OpenGL. I am trying to follow tutorial 101 on subj found on gamedev.net But it crashes at the second string:
GLuint fbo;
glGenFramebuffersEXT(1, &fbo);
With an error (at a string "glGenFramebuffersEXT(1, &fbo);"): Unhandled exception at 0x00000000 in RTT.exe: 0xC0000005: Access violation reading location 0x00000000. I use MS VS 2005.NET (VC 8.0). I've envountered similar problems when tried to create a p-buffer. Please, tell anything that can help, Peter.

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glGenFramebuffersEXT function address hasn't been initialized properly (hence it's NULL address). Are you using something like Glew, or are you getting the address yourself? (Since the program compiles, I assume glGenFramebuffersEXT has been defined somewhere)

~zix

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I load it myself. The code is following:

#include <GL/gl.h>
#undef GL_GLEXT_PROTOTYPES
#include <GL/glext.h>
#include <GL/glut.h>
#include <GL/wglext.h>
#include <glh_genext.h>

PFNGLGENFRAMEBUFFERSEXTPROC glGenFramebuffersEXT = (PFNGLGENFRAMEBUFFERSEXTPROC)wglGetProcAddress("glGenFramebuffersEXT");
PFNGLBINDFRAMEBUFFEREXTPROC glBindFramebufferEXT = (PFNGLBINDFRAMEBUFFEREXTPROC)wglGetProcAddress("BindFramebufferEXT");
PFNGLGENRENDERBUFFERSEXTPROC glGenRenderbuffersEXT = (PFNGLGENRENDERBUFFERSEXTPROC)wglGetProcAddress("GenRenderbuffersEXT");
PFNGLBINDRENDERBUFFEREXTPROC glBindRenderbufferEXT = (PFNGLBINDRENDERBUFFEREXTPROC)wglGetProcAddress("BindRenderbufferEXT");
PFNGLRENDERBUFFERSTORAGEEXTPROC glRenderbufferStorageEXT = (PFNGLRENDERBUFFERSTORAGEEXTPROC)wglGetProcAddress("RenderbufferStorageEXT");
PFNGLFRAMEBUFFERRENDERBUFFEREXTPROC glFramebufferRenderbufferEXT = (PFNGLFRAMEBUFFERRENDERBUFFEREXTPROC)wglGetProcAddress("FramebufferRenderbufferEXT");

And I can't figure out what's wrong here...

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Thanks for assistance.
Looks like I overcame this problem, using one free library. But I will appreciate if you give me some idea why my code was not working.
But I has another problem, while getting into this example. I try to run a simple app (here is the part of it with everything linked to rendering and frame buffers)

void render2texture ()
{
glClearColor ( 1.0, 0.0, 0.0, 1.0 );
glEnable(GL_TEXTURE_2D);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);
glPushAttrib(GL_VIEWPORT_BIT);
glViewport(0,0,512,512);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glColor3d (1.0, 1.0, 1.0);
glutSolidTeapot(1);
glutSwapBuffers();
glPopAttrib();
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}

void display()
{
render2texture();
glClearColor ( 0.0, 0.0, 0.0, 1.0 );
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
//glColor3d (1.0, 1.0, 1.0);
glGenTextures(1, &img);
glBindTexture(GL_TEXTURE_2D, img);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
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_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glGenerateMipmapEXT(GL_TEXTURE_2D);
glColor3d (0.5, 0.5, 0.5);
glBegin( GL_QUADS );
glTexCoord2f(0, 0);
glVertex2f(-1, -1);
glTexCoord2f(0, 1);
glVertex2f(-1, 1);
glTexCoord2f(1, 1);
glVertex2f( 1, 1);
glTexCoord2f(1, 0);
glVertex2f( 1, -1);
glEnd();
glutSwapBuffers();
}

void init()
{
glEnable(GL_TEXTURE_2D);
glClearColor ( 0.0, 0.0, 0.0, 1.0 );
initExtensions();
glGenFramebuffersEXT(1, &fbo);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);

GLuint depthbuffer;
glGenRenderbuffersEXT(1, &depthbuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthbuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, 512, 512);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthbuffer);

glGenTextures(1, &img);
glBindTexture(GL_TEXTURE_2D, img);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, img, 0);
GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
}

void reshape(int w, int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective ( 60.0, (GLfloat)w/(GLfloat)h, 1.0, 60.0 );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt (0, 0, 10, 0, 0, 0, 0, 1, 0);
}

So I want to render to texture blue teapot on red background and then apply it to the quad. I checked if what I want to render into framebuffer renders fine in the screen - that's it. All other code I use from sample.
But the app shows only a black quad (obviously, nothing, because it is on the black background :)). When I disable GL_TEXTURE_2D I can see the gray quad. So the problem is in texture generating/mapping - but I can't find it.
Thanks for everything that could help,
Peter.

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Quote:
Original post by stanlo
Does your framebuffer status equal GL_FRAMEBUFFER_COMPLETE ?

No. My video card is GeForce 5600 FX, so it should support this extension.

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Oops, its value is GL_FRAMEBUFFER_UNSUPPORTED_EXT...
I thought that GeForce 5600 FX supports RTT via frame buffers - but where can be a problem here?

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I think your extension loader isn't working because your missing the prefix 'gl', ie: you have "GenRenderbuffersEXT", and you need "glGenRenderbuffersEXT".

My source looks like

PROC glGetProcAddress(LPCSTR addr){
PROC ret = wglGetProcAddress(addr);
if (ret == NULL)
WriteLogInfo("Unable to load OpenGL Extension %s()", addr);
return ret;
}
void LoadGlExtensions(){
...other extensions...
glGenRenderbuffersEXT = (PFNGLGENRENDERBUFFERSEXTPROC)glGetProcAddress("glGenRenderbuffersEXT");
glDeleteRenderbuffersEXT = (PFNGLDELETERENDERBUFFERSEXTPROC)glGetProcAddress("glDeleteRenderbuffersEXT");
glIsRenderbufferEXT = (PFNGLISRENDERBUFFEREXTPROC)glGetProcAddress("glIsRenderbufferEXT");
glBindRenderbufferEXT = (PFNGLBINDRENDERBUFFEREXTPROC)glGetProcAddress("glBindRenderbufferEXT");
glRenderbufferStorageEXT = (PFNGLRENDERBUFFERSTORAGEEXTPROC)glGetProcAddress("glRenderbufferStorageEXT");
glGetRenderbufferParameterivEXT = (PFNGLGETRENDERBUFFERPARAMETERIVEXTPROC)glGetProcAddress("glGetRenderbufferParameterivEXT");
..etc...
}





It points out if it has any troubling loading of the extensions via my logging function (Which I find handy in debugging it on other computers, as well).

Hope I could help,
~Zix

[Edited by - zix99 on March 27, 2007 2:37:20 PM]

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Quote:
Original post by Garret
So the problem is in texture generating/mapping - but I can't find it.
Thanks for everything that could help,
Peter.


The problem is that you generate and then attach a texture in the init function and then each time you run through the display function you setup a new texture and fill it with nothing and then draw that texture on the quad.

In short; the program is doing what you asked it to.

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