/**

  * $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