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/*******************************************************************
* *
* Using SDL With OpenGL *
* *
* Tutorial by Kyle Foley (sdw) *
* *
* http://gpwiki.org/index.php/SDL:Tutorials:Using_SDL_with_OpenGL *
* *
*******************************************************************/
/*
THIS WORK, INCLUDING THE SOURCE CODE, DOCUMENTATION
AND RELATED MEDIA AND DATA, IS PLACED INTO THE PUBLIC DOMAIN.
THE ORIGINAL AUTHOR IS KYLE FOLEY.
THIS SOFTWARE IS PROVIDED AS-IS WITHOUT WARRANTY
OF ANY KIND, NOT EVEN THE IMPLIED WARRANTY OF
MERCHANTABILITY. THE AUTHOR OF THIS SOFTWARE,
ASSUMES _NO_ RESPONSIBILITY FOR ANY CONSEQUENCE
RESULTING FROM THE USE, MODIFICATION, OR
REDISTRIBUTION OF THIS SOFTWARE.
*/
#include "SDL.h"
#include "SDL_opengl.h"
#include <stdio.h>
#include <string.h>
#define WIDTH 640
#define HEIGHT 480
int main(int argc, char* argv[]) {
SDL_Window* window;
SDL_GLContext context;
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
window = SDL_CreateWindow(
"OpenGL Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, WIDTH, HEIGHT, SDL_WINDOW_OPENGL);
if (!window) {
fprintf(stderr, "Couldn't create window: %s\n", SDL_GetError());
return 0;
}
context = SDL_GL_CreateContext(window);
if (!context) {
fprintf(stderr, "Couldn't create context: %s\n", SDL_GetError());
return 0;
}
#ifndef __EMSCRIPTEN__
// Obtain function pointers.
PFNGLACTIVETEXTUREPROC glActiveTexture_ = (PFNGLACTIVETEXTUREPROC) SDL_GL_GetProcAddress("glActiveTexture");
PFNGLCLIENTACTIVETEXTUREARBPROC glClientActiveTexture_ = (PFNGLCLIENTACTIVETEXTUREARBPROC) SDL_GL_GetProcAddress("glClientActiveTexture");
#else
// Emscripten provides these.
#define glActiveTexture_ glActiveTexture
#define glClientActiveTexture_ glClientActiveTexture
#endif
glMatrixMode(GL_PROJECTION);
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glClearColor(0, 0, 0, 1);
glEnable(GL_TEXTURE_2D);
GLuint texture; // Texture object handle
// Have OpenGL generate a texture object handle for us
glGenTextures(1, &texture);
// Bind the texture object
glBindTexture(GL_TEXTURE_2D, texture);
// Set the texture's stretching properties
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
GLubyte texture_data[] = {
0xffu, 0xffu, 0xffu, 0xffu, // 0.0 0.0
0xffu, 0xffu, 0xffu, 0xffu, // 1.0 0.0
0xffu, 0xffu, 0xffu, 0xffu, // 0.0 1.0
0xffu, 0x00u, 0x00u, 0xffu // 1.0 1.0
};
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 2, 2, 0, GL_RGBA, GL_UNSIGNED_BYTE, texture_data);
// Clear the screen before drawing
glClear(GL_COLOR_BUFFER_BIT);
// Bind the texture to which subsequent calls refer to
glBindTexture(GL_TEXTURE_2D, texture);
const GLenum modes[8] = {
GL_POINTS, GL_LINES, GL_LINE_LOOP, GL_LINE_STRIP,
GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_QUADS
};
const GLfloat vertex_data[4][4] = {
{ 0.25f, 0.25f, 0.0f, 0.0f },
{ 0.75f, 0.25f, 1.0f, 0.0f },
{ 0.25f, 0.75f, 0.0f, 1.0f },
{ 0.75f, 0.75f, 1.0f, 1.0f }
};
const GLushort indices[] = {
0u, 1u, 2u, 2u, 1u, 3u,
};
glVertexPointer(2, GL_FLOAT, sizeof (vertex_data[0]), &vertex_data[0][0]);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(2, GL_FLOAT, sizeof (vertex_data[0]), &vertex_data[0][2]);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
// Set up tex unit 1 state.
glActiveTexture_(GL_TEXTURE0 + 1);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
// Set up tex unit 1 client-side state.
glClientActiveTexture_(GL_TEXTURE0 + 1);
glTexCoordPointer(2, GL_FLOAT, sizeof (vertex_data[0]), &vertex_data[0][2]);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glClientActiveTexture_(GL_TEXTURE0);
// Test GL_TEXTURE matrix mode.
glMatrixMode(GL_TEXTURE);
// Test tex unit 0.
glActiveTexture_(GL_TEXTURE0);
glLoadIdentity();
glRotatef(90, 0.0f, 0.0f, 1.0f);
// Test tex unit 1.
glActiveTexture_(GL_TEXTURE0 + 1);
glLoadIdentity();
glRotatef(270, 0.0f, 0.0f, 1.0f);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);
SDL_GL_SwapWindow(window);
#ifndef __EMSCRIPTEN__
SDL_Event e;
while (SDL_WaitEvent(&e)) {
if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_F12) {
void *pixels = malloc(WIDTH * HEIGHT * 3);
if (pixels) {
glReadBuffer(GL_FRONT);
glReadPixels(0, 0, WIDTH, HEIGHT, GL_RGB, GL_UNSIGNED_BYTE, pixels);
SDL_Surface *surface = SDL_CreateRGBSurfaceWithFormatFrom(pixels, WIDTH, HEIGHT, 32, WIDTH * 3, SDL_PIXELFORMAT_RGB24);
if (surface) {
SDL_SaveBMP(surface, "sdl2_glmatrixmode_texture.bmp");
}
}
}
if (e.type == SDL_QUIT)
break;
}
#endif
// Now we can delete the OpenGL texture and close down SDL
glDeleteTextures(1, &texture);
// Don't quit - we need to reftest the canvas! SDL_Quit();
return 0;
}
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