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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 <stdlib.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);
{
// Also, check getting the error log
const char *fakeVertexShader = "atbute ve4 blarg; ### AAA\n";
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, &fakeVertexShader, NULL);
glCompileShader(vs);
glGetShaderiv(vs, GL_COMPILE_STATUS, &ok);
assert(!ok);
GLint infoLen = 0;
glGetShaderiv(vs, GL_INFO_LOG_LENGTH, &infoLen);
assert(infoLen > 1);
}
}
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
// 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 );
int w = 256, h = 256;
GLushort *pixels = (GLushort*)malloc(w*h*2);
for (int x = 0; x < w; x++)
for (int y = 0; y < h; y++)
pixels[w*y + x] = ((x*32)/w) | ((((w-x)*(h-y)*64)/(w*h)) << 5) | (((y*32)/h) << 11);
// Edit the texture object's image data using the information SDL_Surface gives us
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, w, h, 0,
GL_RGB, GL_UNSIGNED_SHORT_5_6_5, pixels );
// 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;
}
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