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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.
*/
#if !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);
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 );
#if !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 );
// 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. In this test we have each
// attribute in a separate buffer, packed (i.e. stride == 0)
GLfloat vertexData[] = { 10, 10,
300, 10,
300, 128,
10, 128,
410, 10,
600, 10,
630, 200,
310, 250,
100, 300,
300, 300,
300, 400,
100, 400 };
GLfloat textureData[] = { 0, 0,
1, 0,
1, 1,
0, 1,
0, 0.5,
1, 0.5,
1, 1,
0.5, 1,
0, 0,
1, 0,
1, 1,
0, 1, };
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, textureData);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, vertexData);
glDrawArrays(GL_QUADS, 0, 12);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
SDL_GL_SwapBuffers();
#if !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;
}
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