/*******************************************************************
 *                                                                 *
 *                        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, };

    glEnable(GL_TEXTURE_2D); // XXX should be GL_TEXTURE_COORD_ARRAY); and also glEnableClientState! XXX two workarounds here
    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;
}