hi, i’m sorry, i’ve read over the archives the last few days and even played
with the testgl program in the test/ directory of the sdl source package.
yet i still have not been able to find a solution to my problem. i am using
the SDL_OPENGLBLIT mode and i am aware that this is deprecated and should not
be used any longer, but for now i like the convenience of it as opposed to
texturing each image i want to use. i am working on a simple 2D game that
mostly just blits some images to the screen but then occasionally i want to
draw some opengl stuff on top of those images. but no matter what i’ve tried
my opengl does not appear on the screen. everything compiles and runs fine,
but i just never see anything. i think i may just being doing some simple
little thing wrong so i was hoping someone might be able to point out my
mistake since i cannot find it. the frustrating thing is i used to do a
similar thing with the glut but i wanted to start using SDL so that i could
use SDL_Image and use several different types of graphics file formats.
anyway, here is the relevant code and thanks in advance for any help.
// SDL AND OPENGL SETUP
// initialize SDL
if ( SDL_Init( SDL_INIT_VIDEO ) < 0 )
shutdown(“sdl init failed”);
// fetch video info
videoInfo = SDL_GetVideoInfo( );
if(!videoInfo)
shutdown(“video query failed”);
// flags to pass to SDL_SetVideoMode
videoFlags = SDL_OPENGLBLIT; // openGL in SDL
videoFlags |= SDL_GL_DOUBLEBUFFER; // double buffering
// check to see if surfaces can be stored in memory
(videoInfo->hw_available) ? videoFlags |= SDL_HWSURFACE : videoFlags |=
SDL_SWSURFACE;
// check if hardware blits can be done
if(videoInfo->blit_hw)
videoFlags |= SDL_HWACCEL;
// set up OpenGL double buffering
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
// get a SDL surface
if(mainSurface = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP,
videoFlags) == NULL)
shutdown(“set video mode failed”);
// Set the background black
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
// Depth buffer setup
glClearDepth(1.0f);
// Set Line Antialiasing
glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);
// Enable Blending
glEnable( GL_BLEND );
// Type Of Blending To Use
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// Setup our viewport
glViewport(0, 0, (GLint)SCREEN_WIDTH, (GLint)SCREEN_HEIGHT);
// change to the projection matrix and set our viewing volume
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// set ortho view
glOrtho(0.0f, SCREEN_WIDTH, SCREEN_HEIGHT, 0.0f, -1.0f, 1.0f);
// make sure we’re changing model view and not projection
glMatrixMode(GL_MODELVIEW);
// reset view
glLoadIdentity();
// DISPLAY FUNCTION
SDL_BlitSurface(background, NULL, mainSurface, NULL);
SDL_BlitSurface(gameInfoBox, NULL, mainSurface, &gameInfoBoxPosition);
// there are also a bunch of other blits for other images too,
// this is all working great though
if(SDL_LockSurface(mainSurface) != 0) //tried it without this also
shutdown(“sdl surface was not locked\n”);
glEnable(GL_LINE_SMOOTH);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glLineWidth(5.0);
// draw a simple, big red line across the screen, just to test for now
glColor3ub(255,0,0);
glBegin(GL_LINE_STRIP);
glVertex2i(0,0);
glVertex2i(SCREEN_WIDTH,SCREEN_HEIGHT);
glEnd();
SDL_UnlockSurface(mainSurface);
SDL_Flip(mainSurface);
SDL_GL_SwapBuffers();
aaaagh, this is driving me crazy, thanks again for any help or pointers.
-steve
that you might need.