Newbie SDL question (SDL_BlitSurface)

SDL Development
1

I’m trying to add some 2d effects to a GL program I’m working on,
however when anything failed to show up I wrote the following test
program, and I’m completely stumped as to why nothing shows up.--------------------------------------------------------------------
#include <SDL/SDL.h>
#include <SDL/SDL_video.h>
#include <SDL/SDL_image.h>

int main() {
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
printf(“Failed 1\n”);
return 0;
}

SDL_Surface* s = SDL_SetVideoMode(800, 600, 32, SDL_SWSURFACE);
if (!s) {
printf(“Failed 2\n”);
return 0;
}

SDL_Surface* i = IMG_Load(“console.png”);
if (!i) {
printf(“Failed 3\n”);
return 0;
}

SDL_Surface* img = SDL_DisplayFormat(i);
SDL_FreeSurface(i);

SDL_Rect sr = {0, 0, img->w, img->h};
SDL_Rect dr = {10, 10, 0, 0};

if (SDL_BlitSurface(s, &sr, img, &dr) < 0) {
printf(“Failed 4\n”);
return 0;
}

SDL_UpdateRects(s, 1, &dr);

while (1) {
SDL_Event e;
while (SDL_PollEvent(&e))
if (e.type == SDL_QUIT) {
SDL_FreeSurface(s);
SDL_FreeSurface(img);
SDL_Quit();
return 0;
}
}
}

None of the failed messages are printed… A window opens and sits there,
completely black… Can anyone tell me what I’m doing wrong?

Thanks in advance,
Jp Calderone

2

Ok… found the problem in the previous post, the surface order was wrong
in SDL_BlitSurface (oops). But now it’s behaving as my main program does,
which is crashing on the call to SDL_UpdateRects. Here is the new code:----------------------------------------------------------------------------
#include <SDL/SDL.h>
#include <SDL/SDL_video.h>
#include <SDL/SDL_image.h>

int main() {
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
printf(“Failed 1\n”);
return 0;
}

SDL_Surface* s = SDL_SetVideoMode(800, 600, 32, SDL_OPENGL);
if (!s) {
printf(“Failed 2\n”);
return 0;
}

SDL_Surface* img = IMG_Load(“console.png”);
if (!img) {
printf(“Failed 3\n”);
return 0;
}

SDL_Rect dr = {10, 10, img->w, img->h};
if (SDL_BlitSurface(img, NULL, s, &dr) < 0) {
printf(“Failed 4\n”);
return 0;
}
SDL_UpdateRects(s, 1, &dr); // Crash occurs here

while (1) {
SDL_Event e;
while (SDL_PollEvent(&e))
if (e.type == SDL_QUIT) {
SDL_FreeSurface(s);
SDL_FreeSurface(img);
SDL_Quit();
return 0;
}
}
}

Compiled with:
g++ main.cpp -o main sdl-config --cflags --libs -lSDL_image

Again, thanks for any help you can provide,
Jp Calderone

3

From Doc:
SDL_OPENGL Create an OpenGL rendering context. You should have
previously set OpenGL video attributes with SDL_GL_SetAttribute.
SDL_OPENGLBLIT Create an OpenGL rendering context, like above, but
allow normal blitting operations. The screen (2D) surface may have an alpha
channel, and SDL_UpdateRects must be used for updating changes to the screen
surface.

So you must use SDL_OPENGLBLIT

Murlock--------------------
Gloire ? mon saigneur Arioch
http://www.murlock.org

----- Original Message -----
From: kuran@ruinsmud.com (Jp Calderone)
To:
Sent: Tuesday, September 25, 2001 5:50 AM
Subject: Re: [SDL] Newbie SDL question (SDL_BlitSurface)

Ok… found the problem in the previous post, the surface order was wrong
in SDL_BlitSurface (oops). But now it’s behaving as my main program does,
which is crashing on the call to SDL_UpdateRects. Here is the new code:

–

#include <SDL/SDL.h>
#include <SDL/SDL_video.h>
#include <SDL/SDL_image.h>

int main() {
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
printf(“Failed 1\n”);
return 0;
}

SDL_Surface* s = SDL_SetVideoMode(800, 600, 32, SDL_OPENGL);
if (!s) {
printf(“Failed 2\n”);
return 0;
}

SDL_Surface* img = IMG_Load(“console.png”);
if (!img) {
printf(“Failed 3\n”);
return 0;
}

SDL_Rect dr = {10, 10, img->w, img->h};
if (SDL_BlitSurface(img, NULL, s, &dr) < 0) {
printf(“Failed 4\n”);
return 0;
}
SDL_UpdateRects(s, 1, &dr); // Crash occurs here

while (1) {
SDL_Event e;
while (SDL_PollEvent(&e))
if (e.type == SDL_QUIT) {
SDL_FreeSurface(s);
SDL_FreeSurface(img);
SDL_Quit();
return 0;
}
}
}

–

Compiled with:
g++ main.cpp -o main sdl-config --cflags --libs -lSDL_image

Again, thanks for any help you can provide,
Jp Calderone

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl

4

From Doc:
SDL_OPENGL Create an OpenGL rendering context. You should have
previously set OpenGL video attributes with SDL_GL_SetAttribute.
SDL_OPENGLBLIT Create an OpenGL rendering context, like above, but
allow normal blitting operations. The screen (2D) surface may have an alpha
channel, and SDL_UpdateRects must be used for updating changes to the screen
surface.

I must add a caveat:
The SDL_OPENGLBLIT code is very slow, if you can do what you want
to do with OpenGL textures directly, I highly recommend it.

BTW, one of the things I’m doing at Blizzard is writing an optimized 2D
UI that works in a 3D environment, so I know it’s possible. :slight_smile:
(No, it’s not public code, and no, I can’t say anything more about it.)

See ya,
-Sam Lantinga, Software Engineer, Blizzard Entertainment

5

And if someone wants an open-source (LGPL ?ed) Gui for OpenGL,
I?ll point at libUFO ;-)On Tuesday 25 September 2001 09:55, Sam Lantinga wrote:

BTW, one of the things I’m doing at Blizzard is writing an optimized 2D
UI that works in a 3D environment, so I know it’s possible. :slight_smile:
(No, it’s not public code, and no, I can’t say anything more about it.)

–
Johannes Schmidt

< http://libufo.sourceforge.net > Your widget set for OpenGL