The Z-coords for your quad are right at the near culling plane. Try
drawing the quad at a depth of 0.0. You will then probably need to
fiddle with the depth buffer a bit, or the 3d scene you’re trying to
draw might be occluded behind your backing quad.
To start, change those Z coordinates and see if that fixes it. If that
works, before you start drawing things in 3d, to ensure they are not
improperly occluded, I suggest
glDisable(GL_DEPTH_TEST);
/* draw the quad in orthographic projection /
glClear(GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
/ draw my 3d scene */
This will prevent the background from occluding anything drawn later in
3D (if that is what you want…), with pretty good performance. As
others have said, clearing the actual framebuffer isn’t necessary,
because you’re going to draw over it all anyway.
Hello,
After reading all the messages from this thread I have the next
code but i’m not able to display the background bitmap: A BMP,
1024x768, 24 bpp
Any comment ?? And sorry for a lengthy message.
Thanks,
Jorge
//
// This code was created by Jeff Molofee '99
// (ported to SDL by Sam Lantinga '2000)
//
// If you’ve found this code useful, please let me know.
//
// Visit me at www.demonews.com/hosted/nehe
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include “SDL.h”
GLuint textureId;
GLvoid LoadGLTextures(GLvoid)
{
SDL_Surface *image;
image = SDL_LoadBMP( "escenari.bmp" );
if ( image == NULL ) {
fprintf(stderr, "Unable to load background: %s\n", SDL_GetError());
exit(1);
}
glGenTextures(1, &textureId);
glBindTexture(GL_TEXTURE_2D, textureId);
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, 3, image->w, image->h, 0, GL_RGB,
GL_UNSIGNED_BYTE, image->pixels);
gluBuild2DMipmaps(GL_TEXTURE_2D, 3, image->w, image->h, GL_RGB,
GL_UNSIGNED_BYTE, image->pixels);
}
GLvoid InitGL( GLsizei Width, GLsizei Height )
{
glViewport(0, 0, Width, Height);
LoadGLTextures();
glEnable(GL_TEXTURE_2D);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
}
void DrawGLScene( GLsizei Width, GLsizei Height )
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho( 0, Width, Height, 0, -1.0, 1.0 );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glDisable(GL_DEPTH_TEST);
glBindTexture(GL_TEXTURE_2D, textureId);
glBegin(GL_QUADS);
glNormal3f( 0.0f, 0.0f, 1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 0.0f);
glEnd();
glClear(GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
SDL_GL_SwapBuffers();
}
int main(int argc, char **argv)
{
int done;
SDL_Event event;
if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
fprintf(stderr, “Unable to initialize SDL: %s\n”, SDL_GetError());
exit(1);
}
if ( SDL_SetVideoMode(1024, 768, 0, SDL_OPENGL) == NULL ) {
fprintf(stderr, “Unable to create OpenGL screen: %s\n”, SDL_GetError
());
SDL_Quit();
exit(1);
}
InitGL(1024, 768);
/* Loop, drawing and checking events */
done = 0;
while ( !done ) {
DrawGLScene(1024, 768);
while ( SDL_PollEvent(&event) ) {
if ( event.type == SDL_QUIT ) {
done = 1;
}
else if ( event.type == SDL_KEYDOWN ) {
switch ( event.key.keysym.sym ) {
case SDLK_ESCAPE:
done = 1;
break;
default:
break;
}
}
}
}
SDL_Quit();
return 1;
}________________________________________________________________________________
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