void ApplySurface(int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL)
{
SDL_Rect offset;
offset.x = x;
offset.y = y;
SDL_BlitSurface(source, clip, destination, &offset);
}
...
...
for(int col = 0; col < 20; col++)
{
for(int row = 0; row < 15; row++)
{
ApplySurface(col*32, row*32, cell1, map);
/*
if I replace map with screen and remove the
ApplySurface below, it works fine, but I
want to 'build' it to the surface just once and
then just redraw it later as a surface
*/
}
}
ApplySurface(0,0, map, screen);
...
...
if(SDL_Flip(screen) == -1)
{
return 0;
}
...
...
[Solved]SDL black screen
Author
Hey, can anyone tell me why this won't work?
This code shows a black screen.
As I said in the comment in the above code, I want to 'build' the map onto a single SDL surface to draw later, but I don't know or understand why this code doesn't work.
The reason I want to do this is to save processing time, but is it really going to matter?
P.S. sorry if this has been posted before, I wasn't sure what to search for.
[Edited by - Serenity54 on February 29, 2008 4:18:13 PM]
Author
I don't think this will help, but here's the rest of the code.
I believe the problem has something to do with blitting surfaces to a single surface, then blitting that single surface to the surface I want to flip.
//// Global variables//SDL_Event wEvent;SDL_Surface *screen = NULL;//// Initialize SDL//bool Init(char* title, int w, int h, int bpp = 32, Uint32 flags = SDL_DOUBLEBUF|SDL_SWSURFACE){ if(SDL_Init(SDL_INIT_EVERYTHING) == -1) { return false; } screen = SDL_SetVideoMode(w, h, bpp, flags); if(screen == NULL) { return false; } SDL_WM_SetCaption(title, NULL); return true;}//// Kill SDL//void Kill(){ SDL_FreeSurface(screen); SDL_Quit();}//// Load an image from a file//SDL_Surface* LoadImage(char* path){ SDL_Surface *loadedImage = NULL; SDL_Surface *optimizedImage = NULL; //Load image loadedImage = IMG_Load(path); if(loadedImage != NULL) { //optimize optimizedImage = SDL_DisplayFormat(loadedImage); if(optimizedImage != NULL) { //Remove 'magic purple' from the image Uint32 colorkey = SDL_MapRGB(optimizedImage->format, 0xFF, 0, 0xFF); SDL_SetColorKey(optimizedImage,SDL_SRCCOLORKEY, colorkey); } SDL_FreeSurface(loadedImage); } return optimizedImage;}//// Apply an SDL surface to another surface//void ApplySurface(int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL){ SDL_Rect offset; offset.x = x; offset.y = y; SDL_BlitSurface(source, clip, destination, &offset);}//// Mainline//int main(int argc, char* argv[]){ if(!Init("SDL Test", 640, 480, NULL, SDL_SWSURFACE)) // 20 columns, 15 rows { return 1; } SDL_Surface* cell1 = NULL; SDL_Surface* cell2 = NULL; SDL_Surface* map = NULL; cell1=LoadImage("grass_1_night.gif"); cell2=LoadImage("brickwall_1_night.gif"); if(cell1 == NULL || cell2 == NULL) { return 1; } for(int col = 0; col < 20; col++) { for(int row = 0; row < 15; row++) { ApplySurface(col*32, row*32, cell1, map); } } ApplySurface(0,0, map, screen); bool done = false; while(!done) { while(SDL_PollEvent(&wEvent)) { switch(wEvent.type) { case SDL_QUIT: done = true; break; } } if(SDL_Flip(screen) == -1) return 1; } SDL_FreeSurface(cell1); SDL_FreeSurface(cell2); SDL_FreeSurface(map); Kill(); return 0;}I believe the problem has something to do with blitting surfaces to a single surface, then blitting that single surface to the surface I want to flip.
The variable "map" is NULL. To create a surface to blit onto, use SDL_CreateRGBSurface().
Other than that, don't call SDL_FreeSurface on the surface returned by SDL_SetVideoMode(), the documentation expressly says not to.
Other than that, don't call SDL_FreeSurface on the surface returned by SDL_SetVideoMode(), the documentation expressly says not to.
Author
Quote:Original post by rip-off
The variable "map" is NULL. To create a surface to blit onto, use SDL_CreateRGBSurface().
Other than that, don't call SDL_FreeSurface on the surface returned by SDL_SetVideoMode(), the documentation expressly says not to.
Perfect, that fixed it, thanks! What do the last four parameters for SDL_CreateRGBSurface do exactly?
They specify the order of the reg, green, blue and alpha channels. In a 32 bit surface each channel (a byte long) is packed into a single 32 bit integer. I use the example on the linked page, for this:
#if SDL_BYTEORDER == SDL_BIG_ENDIAN rmask = 0xff000000; gmask = 0x00ff0000; bmask = 0x0000ff00; amask = 0x000000ff;#else rmask = 0x000000ff; gmask = 0x0000ff00; bmask = 0x00ff0000; amask = 0xff000000;#endifQuote:Original post by Serenity54
And setting them all to 0 will revert to the systems default? or SDLs default?
Looking at the SDL source, it appears to be a system default. SDL has no default, AFAICT.
This topic is closed to new replies.
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