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/* ----------------------------------------------------------------------- *
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 * This file is part of GEL, http://www.imm.dtu.dk/GEL
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 * Copyright (C) the authors and DTU Informatics
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 * For license and list of authors, see ../../doc/intro.pdf
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 * ----------------------------------------------------------------------- */
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/**
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 * @file glsl_shader.h
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 * @brief Simple functions for loading GLSL shaders.
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 */
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#ifndef __GLGRAPHICS_GLSL_SHADER_H__
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#ifndef __GLGRAPHICS_GLSL_SHADER_H__
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#define __GLGRAPHICS_GLSL_SHADER_H__
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#define __GLGRAPHICS_GLSL_SHADER_H__
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#include <GL/glew.h>
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#include <GL/glew.h>
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#include <string>
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#include <string>
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/* It is a little tricky to make shader programs in C++ using GLSL but the problems are
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/* It is a little tricky to make shader programs in C++ using GLSL but the problems are
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  almost all silly little things. For instance, how do you robustly read from a text
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  almost all silly little things. For instance, how do you robustly read from a text
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  file? How do you compile a shader and check for errors? In OpenGL What is the difference
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  file? How do you compile a shader and check for errors? In OpenGL What is the difference
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  between a GLSL program and a shader anyway?
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  between a GLSL program and a shader anyway?
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  The short answer to the last question is this: A "shader" can be either a vertex shader,
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  The short answer to the last question is this: A "shader" can be either a vertex shader,
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  a geometry shader (in OpenGL 2.0) or a fragment shader. A "program" is a linked combination
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  a geometry shader (in OpenGL 2.0) or a fragment shader. A "program" is a linked combination
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  of these three types of shaders. Note that you don't have to have a geometry shader.
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  of these three types of shaders. Note that you don't have to have a geometry shader.
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  This API attempts to obviate the need for an answer to the first two questions by providing
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  This API attempts to obviate the need for an answer to the first two questions by providing
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  an API for loading and compiling shaders and checking for errors. However, I don't
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  an API for loading and compiling shaders and checking for errors. However, I don't
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  include functions for creating the program, attaching shaders and linking. Why not??!
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  include functions for creating the program, attaching shaders and linking. Why not??!
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  Because the need for flexibility means that the API would be just as complex as just using
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  Because the need for flexibility means that the API would be just as complex as just using
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  the OpenGL functions directly! However, loading shaders and checking for errors in compiled shaders
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  the OpenGL functions directly! However, loading shaders and checking for errors in compiled shaders
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  is different. It makes sense to wrap that. It also makes sense to wrap the error checking for
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  is different. It makes sense to wrap that. It also makes sense to wrap the error checking for
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  programs that are linked, so there is a function for that too.
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  programs that are linked, so there is a function for that too.
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  Since shader loading and error check sandwhich the two calls needed for compilation, the most
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  Since shader loading and error check sandwhich the two calls needed for compilation, the most
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  important function in this API, create_glsl_shader, loads a shader, compiles it, checks for errors
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  important function in this API, create_glsl_shader, loads a shader, compiles it, checks for errors
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  and returns the shader handle. There is also a version which creates a shader from a string.
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  and returns the shader handle. There is also a version which creates a shader from a string.
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  There is some code below to illustrate usage.
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  There is some code below to illustrate usage.
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<code snippet>
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<code snippet>
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  // Create shaders directly from file
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  // Create shaders directly from file
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  GLuint vs = create_glsl_shader(GL_VERTEX_SHADER, shader_path, "tri.vert");
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  GLuint vs = create_glsl_shader(GL_VERTEX_SHADER, shader_path, "tri.vert");
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  GLuint gs = create_glsl_shader(GL_GEOMETRY_SHADER_EXT, shader_path, "tri.geom");
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  GLuint gs = create_glsl_shader(GL_GEOMETRY_SHADER_EXT, shader_path, "tri.geom");
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  GLuint fs = create_glsl_shader(GL_FRAGMENT_SHADER, shader_path, "tri.frag");
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  GLuint fs = create_glsl_shader(GL_FRAGMENT_SHADER, shader_path, "tri.frag");
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  // Create the program
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  // Create the program
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  prog_P0 = glCreateProgram();
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  prog_P0 = glCreateProgram();
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  // Attach all shaders
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  // Attach all shaders
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  if(vs) glAttachShader(prog_P0, vs);
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  if(vs) glAttachShader(prog_P0, vs);
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  if(gs) glAttachShader(prog_P0, gs);
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  if(gs) glAttachShader(prog_P0, gs);
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  if(fs) glAttachShader(prog_P0, fs);
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  if(fs) glAttachShader(prog_P0, fs);
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  // Specify input and output for the geometry shader. Note that this must be
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  // Specify input and output for the geometry shader. Note that this must be
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  // done before linking the program.
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  // done before linking the program.
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_INPUT_TYPE_EXT,GL_TRIANGLES);
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_INPUT_TYPE_EXT,GL_TRIANGLES);
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_VERTICES_OUT_EXT,3);
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_VERTICES_OUT_EXT,3);
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_OUTPUT_TYPE_EXT,GL_TRIANGLE_STRIP);
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  glProgramParameteriEXT(prog_P0,GL_GEOMETRY_OUTPUT_TYPE_EXT,GL_TRIANGLE_STRIP);
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  // Link the program object and print out the info log
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  // Link the program object and print out the info log
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  glLinkProgram(prog_P0);
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  glLinkProgram(prog_P0);
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  print_glsl_program_log(prog_P0);
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  print_glsl_program_log(prog_P0);
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  // Install program object as part of current state
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  // Install program object as part of current state
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  glUseProgram(prog_P0);
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  glUseProgram(prog_P0);
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  // Set the value of a uniform
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  // Set the value of a uniform
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  glUniform2f(glGetUniformLocation(prog_P0,"WIN_SCALE"), win_size_x/2.0, win_size_y/2.0);
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  glUniform2f(glGetUniformLocation(prog_P0,"WIN_SCALE"), win_size_x/2.0, win_size_y/2.0);
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</code snippet>
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</code snippet>
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  Happy shader coding.
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  Happy shader coding.
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  Andreas B¾rentzen, 2007
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  Andreas B¾rentzen, 2007
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  */
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  */
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namespace GLGraphics
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namespace GLGraphics
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{
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{
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  /// Print the info log for a program if the status is not OK.
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  /// Print the info log for a program if the status is not OK.
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  void print_glsl_program_log(GLuint program);
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  void print_glsl_program_log(GLuint program);
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  /// Print the info log for a shader if the status is not OK.
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  /// Print the info log for a shader if the status is not OK.
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  void print_glsl_shader_log(GLuint shader);
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  void print_glsl_shader_log(GLuint shader);
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  /** The two arguments are concatenated to form the name with full path of a text file.
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  /** The two arguments are concatenated to form the name with full path of a text file.
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    This file is read and returned as a string. */
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    This file is read and returned as a string. */
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  const std::string read_glsl_source(const std::string& path, const std::string& file);
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  const std::string read_glsl_source(const std::string& path, const std::string& file);
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  /** Create a shader of type specified by the first argument from a source string given
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  /** Create a shader of type specified by the first argument from a source string given
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    as second argument.  Return shader handle. If there is a problem, the infolog is
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    as second argument.  Return shader handle. If there is a problem, the infolog is
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    printed and 0 is returned (unless the third argument is false). */
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    printed and 0 is returned (unless the third argument is false). */
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  GLuint create_glsl_shader(GLuint stype, const std::string& src, bool print_log = true);
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  GLuint create_glsl_shader(GLuint stype, const std::string& src, bool print_log = true);
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  /** Create a shader of type specified as first argument from the file indicated by the
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  /** Create a shader of type specified as first argument from the file indicated by the
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    supplied path and file name (second and third arguments) and return a shader handle.
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    supplied path and file name (second and third arguments) and return a shader handle.
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    This function is only a convenience function wrapping read_glsl_source and
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    This function is only a convenience function wrapping read_glsl_source and
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    create_glsl_shader */
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    create_glsl_shader */
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  GLuint create_glsl_shader(GLuint stype, const std::string& path, const std::string& file);
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  GLuint create_glsl_shader(GLuint stype, const std::string& path, const std::string& file);
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}
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}
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#endif
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#endif
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