#include "error.h" 

#define OFFSET( P )  ( ( const GLvoid * ) ( sizeof( GLfloat ) * ( P         ) ) )
#define STRIDE       (                    ( sizeof( GLfloat ) * ( 2 + 2 + 4 ) ) )

#define COLOR_0      ( 0 )  // 0 = COLOR_ATTACHMENT0 

#define V_ARRAY      ( 0 )  // 0 = VERTEX_ARRAY
#define T_ARRAY      ( 1 )  // 1 = TEXTURE_COORD_ARRAY
#define C_ARRAY      ( 2 )  // 2 = COLOR_ARRAY

const GLchar *S[] = 
{
    // VS = VERTEX_SHADER
    
#if GL_VERSION_3_2
    "#version 150\n\n"

    "#define ATTRIBUTE in\n"
    "#define VARYING   out\n\n"
#else
    "#ifdef GL_ES\n\n"

    "precision mediump float;\n\n"

    "#endif\n\n"

    "#define ATTRIBUTE attribute\n"
    "#define VARYING   varying\n\n"
#endif // GL_VERSION_3_2

    "ATTRIBUTE vec4 A0;\n"    // A0 = gl_Vertex
    "ATTRIBUTE vec2 A1;\n"    // A1 = gl_MultiTexCoord0.st
    "ATTRIBUTE vec4 A2;\n\n"  // A2 = gl_Color
    
    "VARYING   vec2 V0;\n"    // V0 = gl_TexCoord[0].st
    "VARYING   vec4 V1;\n\n"  // V1 = gl_FrontColor
    
    "uniform   mat4 M0;\n\n"  // M0 = gl_ModelViewProjectionMatrix
        
    "void\n"
    "main( void )\n"
    "{\n"
        "\tV0          = vec2(      A1 );\n"
        "\tV1          = vec4(      A2 );\n\n"
        
        "\tgl_Position = vec4( M0 * A0 );\n"
    "}\n",
    
    // FS = FRAGMENT_SHADER
    
#if GL_VERSION_3_2
    "#version 150\n\n"

    "#define VARYING in\n"
#else
    "#ifdef GL_ES\n\n"

    "precision mediump float;\n"
    "precision lowp    sampler2D;\n\n"

    "#endif\n\n"

    "#define VARYING varying\n\n"

    "#define O0      gl_FragColor\n\n"
#endif // GL_VERSION_3_2

    "uniform sampler2D S0;\n\n"
    
    "VARYING vec2      V0;\n"    // V0 = gl_TexCoord[0].st
    "VARYING vec4      V1;\n"    // V1 = gl_Color
    
#if GL_VERSION_3_2
    "out     vec4      O0;\n\n"  // O0 = gl_FragColor
#else
    "\n"
#endif // GL_VERSION_3_2

    "void\n"
    "main( void )\n"
    "{\n"
        "\tO0 = vec4( V1 * texture2D( S0, V0 ) );\n"
    "}\n",
};

GLuint PID, VID, FID, UID, TID, AID, VAO, VBO, IBO, FBO, VAO; 

// SETUP STATE
{
    // Generate (shader, texture, buffer) IDs.
    {
        PID = glCreateProgram( ); VID = glCreateShader( GL_VERTEX_SHADER ); FID = glCreateShader( GL_FRAGMENT_SHADER );
        
        glGenTextures    ( 1, &TID );
        glGenTextures    ( 1, &AID );

        glGenBuffers     ( 1, &VBO );
        glGenBuffers     ( 1, &IBO );
        glGenFramebuffers( 1, &FBO );

#if GL_VERSION_3_2
        glGenVertexArrays( 1, &VAO );
#endif // GL_VERSION_3_2

    }

    // Compile VS, FS and setup attributes. 
    {
        glShaderSource( VID, 1, &S[0], NULL ); glCompileShader( VID ); GetShaderInfoLog( VID, S[0] ); glAttachShader( PID, VID );
        glShaderSource( FID, 1, &S[1], NULL ); glCompileShader( FID ); GetShaderInfoLog( FID, S[1] ); glAttachShader( PID, FID );

#if GL_VERSION_3_2
        glBindFragDataLocation( PID, COLOR_0, "O0" );  // O0 = gl_FragColor,        Only needed for indices > 0.
#endif // GL_VERSION_3_2            

        glBindAttribLocation  ( PID, V_ARRAY, "A0" );  // A0 = gl_Vertex,           Only needed for indices > 0.
        glBindAttribLocation  ( PID, T_ARRAY, "A1" );  // A1 = glMultiTexCoord0.st, Only needed for indices > 0.
        glBindAttribLocation  ( PID, C_ARRAY, "A2" );  // A2 = gl_Color,            Only needed for indices > 0.

        glLinkProgram( PID );   
                
            // TODO: Check for program errors here.
                    
                glUseProgram( PID ); 
    }

    // Setup uniform (matrix, sampler) state.
    {
        const GLfloat MVP[16] = { ... };  // Assumes ( MV * P ) matrix.
        
        glUniformMatrix4fv( ( UID = glGetUniformLocation( PID, "M0" ) ), 1, GL_FALSE, MVP );
        glUniform1i       ( (       glGetUniformLocation( PID, "S0" ) ), 0                );  // Only needed for units > GL_TEXTURE0.
    }

    // Setup VA, IA state and attribute offsets.
    {
        const GLfloat  VA[ ] = { ... };  // Assumes interleaved { ..., X, Y, S, T, R, G, B, A, ... } (float ) vertex array.
        
        const GLushort IA[ ] = { ... };  // Assumes { ..., (N + 0), (N + 1), (N + 2), (N + 3), ... } (ushort) index  array.
        
#if GL_VERSION_3_2
        glBindVertexArray(                          VAO );
#endif // GL_VERSION_3_2

        glBindBuffer     ( GL_ARRAY_BUFFER,         VBO ); glBufferData( GL_ARRAY_BUFFER,         sizeof( VA ), VA, GL_STATIC_DRAW );
        glBindBuffer     ( GL_ELEMENT_ARRAY_BUFFER, IBO ); glBufferData( GL_ELEMENT_ARRAY_BUFFER, sizeof( IA ), IA, GL_STATIC_DRAW );

        glEnableVertexAttribArray( V_ARRAY ); glVertexAttribPointer( V_ARRAY, 2, GL_FLOAT, GL_FALSE, STRIDE, OFFSET( 0 ) );  // A0 = gl_Vertex
        glEnableVertexAttribArray( T_ARRAY ); glVertexAttribPointer( T_ARRAY, 2, GL_FLOAT, GL_FALSE, STRIDE, OFFSET( 2 ) );  // A1 = glMultiTexCoord0.st
        glEnableVertexAttribArray( C_ARRAY ); glVertexAttribPointer( C_ARRAY, 4, GL_FLOAT, GL_FALSE, STRIDE, OFFSET( 4 ) );  // A2 = gl_Color
    }

    // Setup texture state.
    {
        GLubyte *P = calloc( 1, ( W * H * 4 * sizeof( GLubyte ) ) );
        
        {
            // TODO: Fill pixel buffer.
        }
        
        glActiveTexture( GL_TEXTURE0        );
        glBindTexture  ( GL_TEXTURE_2D, TID );

        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR        );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR        );  // Only needed for (non default) NEAREST.
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,     GL_CLAMP_TO_EDGE );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,     GL_CLAMP_TO_EDGE );
        
        glTexImage2D   ( GL_TEXTURE_2D, 0, GL_RGBA, W, H, 0, GL_RGBA, GL_UNSIGNED_BYTE, P );
        
        free( P );
    }

    // Setup framebuffer state (assumes support for GL_ARB_framebuffer_object).
    {
        glActiveTexture  ( GL_TEXTURE0         );
        glBindTexture    ( GL_TEXTURE_2D,  AID );  // Source.
        glBindFramebuffer( GL_FRAMEBUFFER, FBO );  // Destination.

        glTexParameteri  ( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR        );
        glTexParameteri  ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR        );  // Only needed for (non default) NEAREST.
        glTexParameteri  ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,     GL_CLAMP_TO_EDGE );
        glTexParameteri  ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,     GL_CLAMP_TO_EDGE );
        
        glTexImage2D     ( GL_TEXTURE_2D, 0, GL_RGBA, W, H, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL );

        glFramebufferTexture2D( GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, AID, 0 );

        CheckFramebufferStatus( );
    }
}

// RENDER STATE
{
    // Only needed for render to texture case.
    {
        glBindFramebuffer( GL_FRAMEBUFFER, FBO );

        // Only needed for multiple texture case.
        {
            glActiveTexture( GL_TEXTURE0        );
            glBindTexture  ( GL_TEXTURE_2D, TID );
            
            // Only needed for multiple buffer case.
            {

#if GL_VERSION_3_2
                glBindVertexArray(                          VAO );
#else
                glBindBuffer     ( GL_ARRAY_BUFFER,         VBO );  
                glBindBuffer     ( GL_ELEMENT_ARRAY_BUFFER, IBO );
#endif // GL_VERSION_3_2

                // Only needed for multiple program case.
                {
                    glUseProgram      ( PID                   );
                    glUniformMatrix4fv( UID, 1, GL_FALSE, MVP );  // Only needed for MVP updates.
					
                    // Render primitives.
                    {
                        glDrawElements( GL_TRIANGLE_STRIP, ..., GL_UNSIGNED_SHORT, NULL );
                    }
                }
            }
        }       
    }
}