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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.
*/
#ifndef __EMSCRIPTEN__
#define USE_GLEW 1
#endif
#if USE_GLEW
#include "GL/glew.h"
#endif
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#if !USE_GLEW
#include "SDL/SDL_opengl.h"
#endif
#include <stdio.h>
#include <string.h>
#include <assert.h>
void shaders() {
#if USE_GLEW
glewInit();
#endif
GLint ok;
const char *vertexShader = "void main(void) \n"
"{ \n"
" gl_Position = ftransform(); \n"
" gl_TexCoord[0] = gl_MultiTexCoord0; \n"
" gl_FrontColor = gl_Color; \n"
"} \n";
const char *fragmentShader = "uniform sampler2D tex0; \n"
"void main(void) \n"
"{ \n"
" gl_FragColor = gl_Color * texture2D(tex0, gl_TexCoord[0].xy); \n"
"} \n";
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, &vertexShader, NULL);
glCompileShader(vs);
glGetShaderiv(vs, GL_COMPILE_STATUS, &ok);
assert(ok);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, &fragmentShader, NULL);
glCompileShader(fs);
glGetShaderiv(fs, GL_COMPILE_STATUS, &ok);
assert(ok);
GLuint program = glCreateProgram();
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glGetProgramiv(program, GL_LINK_STATUS, &ok);
assert(ok);
assert(glIsProgram(program));
assert(!glIsProgram(0));
assert(!glIsProgram(program+1)); // a number that can't be a real shader
glUseProgram(program);
}
int main(int argc, char *argv[])
{
SDL_Surface *screen;
// Slightly different SDL initialization
if ( SDL_Init(SDL_INIT_VIDEO) != 0 ) {
printf("Unable to initialize SDL: %s\n", SDL_GetError());
return 1;
}
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 ); // *new*
screen = SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL ); // *changed*
if ( !screen ) {
printf("Unable to set video mode: %s\n", SDL_GetError());
return 1;
}
// Set the OpenGL state after creating the context with SDL_SetVideoMode
glClearColor( 0, 0, 0, 0 );
#ifndef __EMSCRIPTEN__
glEnable( GL_TEXTURE_2D ); // Need this to display a texture XXX unnecessary in OpenGL ES 2.0/WebGL
#endif
glViewport( 0, 0, 640, 480 );
glMatrixMode( GL_PROJECTION );
GLfloat matrixData[] = { 2.0/640, 0, 0, 0,
0, -2.0/480, 0, 0,
0, 0, -1, 0,
-1, 1, 0, 1 };
glLoadMatrixf(matrixData); // test loadmatrix
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
// Load the OpenGL texture
GLuint texture; // Texture object handle
SDL_Surface *surface; // Gives us the information to make the texture
if ( (surface = IMG_Load("screenshot.png")) ) {
// Check that the image's width is a power of 2
if ( (surface->w & (surface->w - 1)) != 0 ) {
printf("warning: image.bmp's width is not a power of 2\n");
}
// Also check if the height is a power of 2
if ( (surface->h & (surface->h - 1)) != 0 ) {
printf("warning: image.bmp's height is not a power of 2\n");
}
// Have OpenGL generate a texture object handle for us
glGenTextures( 1, &texture );
// Test binding null
glBindTexture( GL_TEXTURE_2D, 0 );
// Bind the texture object
glBindTexture( GL_TEXTURE_2D, texture );
// Set the texture's stretching properties
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
//SDL_LockSurface(surface);
// Add some greyness
memset(surface->pixels, 0x66, surface->w*surface->h);
// Edit the texture object's image data using the information SDL_Surface gives us
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, surface->w, surface->h, 0,
GL_RGBA, GL_UNSIGNED_BYTE, surface->pixels );
//SDL_UnlockSurface(surface);
}
else {
printf("SDL could not load image.bmp: %s\n", SDL_GetError());
SDL_Quit();
return 1;
}
// Free the SDL_Surface only if it was successfully created
if ( surface ) {
SDL_FreeSurface( surface );
}
// Clear the screen before drawing
glClear( GL_COLOR_BUFFER_BIT );
shaders();
// Bind the texture to which subsequent calls refer to
glBindTexture( GL_TEXTURE_2D, texture );
// Use clientside vertex pointers to render two items
GLfloat vertexData[] = { 0, 0, 10, 10, // texture2, position2
1, 0, 300, 10,
1, 1, 300, 128,
0, 1, 10, 128,
0, 0.5, 410, 10,
1, 0.5, 600, 10,
1, 1, 630, 200,
0.5, 1, 310, 250,
0, 0, 100, 300,
1, 0, 300, 300,
1, 1, 300, 400,
0, 1, 100, 400 };
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 4*4, &vertexData[0]);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 4*4, &vertexData[2]);
glDrawArrays(GL_QUADS, 0, 12);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
SDL_GL_SwapBuffers();
#ifndef __EMSCRIPTEN__
// Wait for 3 seconds to give us a chance to see the image
SDL_Delay(3000);
#endif
// Now we can delete the OpenGL texture and close down SDL
glDeleteTextures( 1, &texture );
SDL_Quit();
return 0;
}