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rafaelmgn

[SDL] How to copy the screen to another surface?

14 posts in this topic

Hello!

I'm trying to make a copy of the actual screen to another SDL_Surface. I tried to use SDL_BlitSurface and SDL_DisplayFormat, rounded and non-rounded by callings of SDL_LockSurface and SDL_UnlockSurface, but I can't get the copy. I only get an empty surface.

Anyone can help me?
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SDL_BlitSurface() should work, without SDL_LockSurface(). How are you allocating the destination surface? Have you tried checking the return value of SDL_BlitSurface(), and the value of SDL_GetError()?
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I did the following:

[code]SDL_Surface *mySurface, *temp;
SDL_Rect rect;

temp = SDL_CreateRGBSurface(SDL_SWSURFACE | SDL_SRCALPHA, screen->w, screen->h, 0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF);

if (temp) {
mySurface = SDL_DisplayFormat(temp);
SDL_FreeSurface(temp);
}

rect.x = 0;
rect.y = 0;

SDL_BlitSurface(screen, NULL, mySurface, &rect);[/code]

I tried to use SDL_GetError() but it didn't returned anything.
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SDL_CreateRGBSurface takes 8 arguments but you only pass 7 arguments. How is that possible?

SDL_DisplayFormat creates a copy so all you should have to do to create a copy of the screen surface is[code]mySurface = SDL_DisplayFormat(screen);[/code]
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Sorry, I mistyped that line:

[code]temp = SDL_CreateRGBSurface(SDL_SWSURFACE | SDL_SRCALPHA, screen->w, screen->h, 32, 0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF);
[/code]

I tried to use SDL_DisplayFormat, but no result and no error... [img]http://public.gamedev.net/public/style_emoticons/default/huh.gif[/img]
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Sorry, I just put a fragment of the code, just a explanation of what I'm doing...

[code]SDL_Surface *mySurface, *temp;
SDL_Rect rect;

temp = SDL_CreateRGBSurface(SDL_SWSURFACE | SDL_SRCALPHA, screen->w, screen->h, 32, 0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF);

if (temp) {
mySurface = SDL_DisplayFormat(temp);
SDL_FreeSurface(temp);
}

rect.x = 0;
rect.y = 0;

SDL_BlitSurface(screen, NULL, mySurface, &rect);

if (!mySurface) {
cerr << string(SDL_GetError()) << endl;
exit(-1);
}[/code]

It pass through the 'if'... there's no error, but it gives me a black surface.
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When you say no result, do you mean that SDL_DisplayFormat returns NULL?
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In your code SDL_DisplayFormat should return a blank surface because you haven't copied the screen surface yet.
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It is probably easier if you make a testcase: A small program that compiles and have the same problem you want to show. Because now we are only guessing.
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Here is such a reasonably minimal example:
[code]
#include "SDL.h"
#include <iostream>
#include <cstdlib>
#include <ctime>

int main(int, char **)
{
std::srand(static_cast<unsigned>(std::time(0)));

if(SDL_Init(SDL_INIT_VIDEO) < 0)
{
std::cerr << "Failed to initialise SDL: " << SDL_GetError() << '\n';
return 1;
}

std::atexit(&SDL_Quit);

SDL_Surface *screen = SDL_SetVideoMode(400, 400, 0, 0);
if(!screen)
{
std::cerr << "Failed to initialise SDL: " << SDL_GetError() << '\n';
return 1;
}

bool running = true;
while(running)
{
SDL_Event event;
if(SDL_WaitEvent(&event))
{
if(event.type == SDL_QUIT)
{
running = false;
}
else if((event.type == SDL_KEYUP) && (event.key.keysym.sym == SDLK_ESCAPE))
{
running = false;
}
}

SDL_FillRect(screen, NULL, 0);

for(int i = 0 ; i < 10 ; ++i)
{
SDL_Rect r;
r.w = ((std::rand() % 5) + 1) * 10;
r.h = ((std::rand() % 5) + 1) * 10;
r.x = std::rand() % (screen->w - r.w);
r.y = std::rand() % (screen->h - r.h);
SDL_FillRect(screen, &r, SDL_MapRGB(screen->format, 0xff * ((i % 3) == 0), 0xff * ((i % 3) == 1), 0xff * ((i % 3) == 2)));
}

SDL_Flip(screen);
}

SDL_Surface *copy = SDL_DisplayFormat(screen);
if(!copy)
{
std::cerr << "Failed to copy surface: " << SDL_GetError() << '\n';
return 1;
}

if(SDL_SaveBMP(copy, "out.bmp") != 0)
{
std::cerr << "Failed to save output: " << SDL_GetError() << '\n';
return 1;
}

std::cout << "Success!\n";
return 0;
}
[/code]
Works for me[sup]TM[/sup].
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I deleted all my code, and started again. It worked... [img]http://public.gamedev.net/public/style_emoticons/default/mellow.gif[/img]
I used SDL_DisplayFormat to convert the screen to another surface.

Thanks guys
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