/**

 * $Id: gl_sl.c,v 1.1 2007-09-28 07:24:14 nkeynes Exp $

 *

 * GLSL shader loader/unloader. Current version assumes there's exactly

 * 1 shader program that's used globally. This may turn out not to be the

 * most efficient approach.

 *

 * Copyright (c) 2007 Nathan Keynes.

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 */

#include <GL/gl.h>

#include <GL/glext.h>

#include "drivers/gl_common.h"

#include "display.h"

#define MAX_ERROR_BUF 4096

static GLuint glsl_program, glsl_vert_shader, glsl_frag_shader;

gboolean glsl_is_supported()

{

    return isGLExtensionSupported("GL_ARB_fragment_shader") &&

	isGLExtensionSupported("GL_ARB_vertex_shader") &&

	isGLExtensionSupported("GL_ARB_shading_language_100");

}

#ifdef GL_ARB_shader_objects

void glsl_print_error( char *msg, GLhandleARB obj )

{

    char buf[MAX_ERROR_BUF];

    GLsizei length;

    glGetInfoLogARB( obj, sizeof(buf), &length, buf );

    ERROR( "%s: %s", msg, buf );

}

gboolean glsl_check_shader_error( char *msg, GLhandleARB obj )

{

    GLint value;

    glGetObjectParameterivARB(obj, GL_OBJECT_COMPILE_STATUS_ARB, &value);

    if( value == 0 ) {

	glsl_print_error(msg, obj);

	return FALSE;

    }

    return TRUE;

}

gboolean glsl_check_program_error( char *msg, GLhandleARB obj )

{

    if( glGetError() != GL_NO_ERROR ) {

	glsl_print_error(msg, obj);

    }

    return TRUE;

}

gboolean glsl_load_shaders( const char *vertex_src, const char *fragment_src )

{

    gboolean vsok, fsok, pok = FALSE;

    glsl_program = glCreateProgramObjectARB();

    glsl_vert_shader = glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);

    glsl_frag_shader = glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);

    glShaderSourceARB( glsl_vert_shader, 1, &vertex_src, NULL );

    glCompileShaderARB(glsl_vert_shader);

    vsok = glsl_check_shader_error("Failed to compile vertex shader", glsl_vert_shader);

    glShaderSourceARB( glsl_frag_shader, 1, &fragment_src, NULL );

    glCompileShaderARB(glsl_frag_shader);

    fsok = glsl_check_shader_error("Failed to compile fragment shader", glsl_frag_shader);

    if( vsok && fsok ) {

	glAttachObjectARB(glsl_program, glsl_vert_shader);

	glAttachObjectARB(glsl_program, glsl_frag_shader);

	glLinkProgramARB(glsl_program);

	pok = glsl_check_program_error( "Failed to link shader program", glsl_program );

    }

    if( pok ) {

	glUseProgramObjectARB(glsl_program);

	pok = glsl_check_program_error( "Failed to apply shader program", glsl_program );

    } else {

	glsl_unload_shaders();

    }

    return pok;

}

void glsl_unload_shaders(void)

{

    glUseProgramObjectARB(0);

    glDetachObjectARB(glsl_program, glsl_vert_shader);

    glDetachObjectARB(glsl_program, glsl_frag_shader);

    glDeleteObjectARB(glsl_program);

    glDeleteObjectARB(glsl_vert_shader);

    glDeleteObjectARB(glsl_frag_shader);

}

#else

gboolean glsl_check_shader_error( char *msg, GLuint shader )

{

    GLint value;

    glGetShaderiv( shader, GL_COMPILE_STATUS, &value );

    if( value == 0 ) {

	char buf[MAX_ERROR_BUF];

	GLsizei length;

	glGetShaderInfoLog( shader, sizeof(buf), &length, buf );

	ERROR( "%s: %s", msg, buf );

	return FALSE;

    }

    return TRUE;

}

gboolean glsl_check_program_error( char *msg, GLuint program )

{

    if( glGetError() != GL_NO_ERROR ) {

	char buf[MAX_ERROR_BUF];

	GLsizei length;

	glGetProgramInfoLog( program, sizeof(buf), &length, buf );

	ERROR( "%s: %s", msg, buf );

	return FALSE;

    }

    return TRUE;

}

gboolean glsl_load_shaders( const char *vertex_src, const char *fragment_src )

{

    gboolean vsok, fsok, pok = FALSE;

    glsl_program = glCreateProgram();

    glsl_vert_shader = glCreateShader(GL_VERTEX_SHADER);

    glsl_frag_shader = glCreateShader(GL_FRAGMENT_SHADER);

    glShaderSource( glsl_vert_shader, 1, &vertex_src, NULL );

    glCompileShader(glsl_vert_shader);

    vsok = glsl_check_shader_error( "Failed to compile vertex shader", glsl_vert_shader );

    glShaderSource( glsl_frag_shader, 1, &fragment_src, NULL );

    glCompileShader(glsl_frag_shader);

    fsok = glsl_check_shader_error( "Failed to compile fragment shader", glsl_frag_shader );

    if( vsok && fsok ) {

	glAttachShader(glsl_program, glsl_vert_shader);

	glAttachShader(glsl_program, glsl_frag_shader);

	glLinkProgram(glsl_program);

	pok = glsl_check_program_error( "Failed to link shader program", glsl_program );

    }

    if( pok ) {

	glUseProgram(glsl_program);

    } else {

	glsl_unload_shaders();

    }

    return pok;

}

void glsl_unload_shaders(void)

{

    glUseProgram(0);

    glDetachShader(glsl_program, glsl_vert_shader);

    glDetachShader(glsl_program, glsl_frag_shader);

    glDeleteProgram(glsl_program);

    glDeleteShader(glsl_vert_shader);

    glDeleteShader(glsl_frag_shader);

}

#endif