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OpenGL [SOLVED] problems with render-to-texture

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There seems to be problems when creating a texture dynamically that is larger than the screen size. I am just a rookie in OpenGL but there must be a problem with the glViewport call to resize it to fit the texture I am creating. Edit: I forgot to add, I am using glCopyTexImage2D. I have two images to show the problem. Ok Not ok As you can see where the small letters begin they are not displayed correctly when used. As for now, I am not using any call to glViewport at all because using glViewport( 0, 0, theWidthOfTexture, theHeightOfTexture ) displays nothing. Are there any pitfalls in using this or should I paste some code? [Edited by - energydrink on April 24, 2010 4:39:13 PM]

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Why not use FBOs to do RTT? They easily support textures larger than the screen.

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I looked into FBO and yes, it is probably what I need. However, after reading up on the subject there seems not to working. I am sure there is a minor problem or have I missed the concept?

I am basically using the same code as with glCopyTexImage2D. The following code is only called once when creating a dynamic texture for a fontsheet.

Notice I have no texture parameters here


myFontTexID.push_back( 0 ); //Allocate new space for texture reference
glGenTextures( 1, &myFontTexID[ myFontTexID.size() - 1 ] );
glBindTexture( GL_TEXTURE_2D, myFontTexID[ myFontTexID.size() - 1 ] );
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, ( GLsizei )totalWidth, ( GLsizei )totalHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL );

The following buffer setup should be correctly executed, right?


GLuint framebuffer;
glGenFramebuffers( 1, &framebuffer );
glBindFramebuffer( GL_FRAMEBUFFER_EXT, framebuffer );

GLuint renderbuffer;
glGenRenderbuffers( 1, &renderbuffer );
glBindRenderbuffer( GL_RENDERBUFFER_EXT, renderbuffer );

//Create storage for image data
glRenderbufferStorage( GL_RENDERBUFFER_EXT, GL_RGBA, ( GLsizei )totalWidth, ( GLsizei )totalHeight );
//Attach renderbuffer to currently bound framebuffer
//Attach texture to FBO
glFramebufferTexture2D( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, myFontTexID[ myFontTexID.size() - 1 ], 0 );

Here is if I got the concept correctly. With glCopyTexImage2D it was easy to understand, it was basically a printscreen call. However with FBO I am now assuming that everything that gets rendered will be put into the renderbuffer which is attached to the framebuffer which is atteched to the "main"texture. There is no call like when using VBO like glBufferData where you actually have a command to upload the current information.

Since this is in the same method, the framebuffer should be already bound.


glViewport( 0, 0, totalWidth, totalHeight ); //Set size of texture

GLfloat x = 0.0f;
GLuint tempTex;
glGenTextures( 1, &tempTex );
glBindTexture( GL_TEXTURE_2D, tempTex );

glClear( GL_COLOR_BUFFER_BIT ); //Clear everything before drawing
for( GLuint i = 0; i < myAsciiTable.length(); i++ ) {
character = myAsciiTable[ i ];

//Create temporary texture
SDL_Surface *tempSurf = TTF_RenderText_Blended( myLoadedFont, character.c_str(), color );
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, tempSurf->w, tempSurf->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, tempSurf->pixels );

//Advance one glyph size
glTranslatef( x, 0.0f, 0.0f );
x += ( GLfloat )tempSurf->w;

glBegin( GL_QUADS );
glTexCoord2f( 0.0f, 1.0f ); glVertex2f( 0.0f, 0.0f );
glTexCoord2f( 0.0f, 0.0f ); glVertex2f( 0.0f, ( GLfloat )tempSurf->h );
glTexCoord2f( 1.0f, 0.0f ); glVertex2f( ( GLfloat )tempSurf->w, ( GLfloat )tempSurf->h );
glTexCoord2f( 1.0f, 1.0f ); glVertex2f( ( GLfloat )tempSurf->w, 0.0f );

SDL_FreeSurface( tempSurf );
glBindFramebuffer( GL_FRAMEBUFFER_EXT, 0 );


glViewport( 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT );

glDeleteFramebuffers( 1, &framebuffer );
glDeleteRenderbuffers( 1, &renderbuffer );

This displays only white quads with no texture. If you recall what I wrote before my "create texture" code, I have no texture parameters. Setting a MIN and MAG filter will just end up displaying nothing.

Help! :)

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You don't need a renderbuffer, just attach a texture to the FBO.
Set the MIN/MAG filters to something, like NEAREST, before glTexImage2D. Else, your texture will be incomplete (as the default is mipmapped, and you don't have mipmaps).

This should make it work.

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Thanks for fast reply. It sort of work. First it displays nothing, removing glViewport() will display text on the screen. However, the texture is larger than the screen and therefor not getting the whole texture. This was also the case when I used glCopyTexImage2D, using glViewport() would display nothing.

Using my "setOrtho2D" method was the only way to get it to work.

glViewport( 0, 0, width, height );
glMatrixMode( GL_PROJECTION );
gluOrtho2D( 0, width, 0, height );

Is there a reason I have to call my gluOrtho2D aswell? ( I am not using perspective, only 2D )

In anyway, it is working! Ah, finally! BIG thank you! :)

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