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MichaelBarth

OpenGL Having trouble getting an image on screen

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Alright, I've sort of touched on this question before, and also I wasn't sure whether or not to put this in the OpenGL or SDL section since I'm using SDL_OpenGL.

Anyway, here's my problem, I have code that loads an SDL_Surface and converts it to a GLuint. It worked fine... with the particular image I was testing it with.

It works just fine with this image: nukeico.png

However I've tried a few other images (that were 1920 x 1200) with different depths, with transparent pixels, and different image formats. Only this particular image works.

Visual Studio comes up with an error: "Unhandled exception at 0x00f81841 in NAMEOFGAME.exe: 0xC0000005: Access violation reading location 0x0614b000."

Here's my code:


GLuint loadTexture ( char *filename )
{
GLuint retval;
SDL_Surface *sdlimage;
void *raw;
int w, h, i, j, bpp;
Uint8 *srcPixel, *dstPixel;
Uint32 truePixel;
GLenum errorCode;

sdlimage = IMG_Load(filename);

if ( !sdlimage ) {
printf("SDL_Image load error: %s\n", IMG_GetError());
return 0;
}
if ( sdlimage->format->BytesPerPixel < 2 ) {
printf("Bad image -- not true color!\n");
return 0;
}
w = sdlimage->w;
h = sdlimage->h;
raw = (void *)malloc( w * h * 4 );
dstPixel = (Uint8 *)raw;
SDL_LockSurface( sdlimage );
bpp = sdlimage->format->BytesPerPixel;

//It seems to crash within this for loop:
for ( i = h ; i > 0 ; i-- ) {

for ( j = 0 ; j < w ; j++ ) {
srcPixel = (Uint8 *)sdlimage->pixels + i * sdlimage->pitch + j * bpp;
switch (bpp) {
case 1:
truePixel = *srcPixel;
break;
case 2:
truePixel = *(Uint16 *)srcPixel;
break;
case 3:
if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
truePixel = srcPixel[0] << 16 | srcPixel[1] << 8 | srcPixel[2];
} else {
truePixel = srcPixel[0] | srcPixel[1] << 8 | srcPixel[2] << 16;
}
break;
case 4:
truePixel = *(Uint32 *)srcPixel;
break;
default:
printf("Image bpp of %d unusable\n", bpp);
return 0;
break;
}
SDL_GetRGBA( truePixel, sdlimage->format, &(dstPixel[0]), &(dstPixel[1]), &(dstPixel[2]), &(dstPixel[3]));
dstPixel++;
dstPixel++;
dstPixel++;
dstPixel++;
}
}
SDL_UnlockSurface( sdlimage );
SDL_FreeSurface( sdlimage );
while ( glGetError() ) { ; }
glGenTextures( 1, &retval );
glBindTexture( GL_TEXTURE_2D, retval );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
errorCode = glGetError();
if ( errorCode != 0 ) {
if ( errorCode == GL_OUT_OF_MEMORY ) {
printf("Out of texture memory!\n");
}
return 0;
}
gluBuild2DMipmaps( GL_TEXTURE_2D, 4, w, h, GL_RGBA, GL_UNSIGNED_BYTE, (Uint8 *)raw);
errorCode = glGetError();
if ( errorCode != 0 ) {
if ( errorCode == GL_OUT_OF_MEMORY ) {
printf("Out of texture memory!\n");
}
return 0;
}
return retval;
}


I wrote a comment at the for loop at which it crashes, it seems to crash determining the BPP. Any help is appreciated.

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Have you tried running the debugger to pinpoint the crash location and the variable values at the time?

Suspiciously it works on a what looks like square image, while failing on other non-square images, so my guess is that you've got something broken with your loop that you've commented on. Pull up the debugger and see what's going on.

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