program_id=loadOpenGLShader(filename_fs,filename_vs)

function program_id=loadOpenGLShader(filename_fs,filename_vs)
% loadOpenGLShader will load a vertex and fragment shader in to a GLSL
% program.
%
% program_id = loadOpenGLShader(filename_FragmentShader,filename_VertexShader)
%
% inputs,
%   filename_FragmentShader : The filename of the fragmentShader or [] in
%                                   case of only needing a vertex shader.
%   filename_VertexShader : The filename of the vertexShader 
%
% ouputs,
%   program_id : The id of a GLSL program. (Gl.glUseProgram(program_id))
%                           
% example,
%   program_id=loadOpenGLShader('fragment_program.glsl','vertex_program.glsl');
%   % Use / Enable the shader code
%   Gl.glUseProgram(program_id);
%
% Function is written by D.Kroon University of Twente (April 2009)


import Tao.OpenGl.*

% Process inputs
if(~exist('filename_fs','var')), filename_fs=[]; end
if(~exist('filename_vs','var')), filename_vs=[]; end

% Create program (id)
program_id = Gl.glCreateProgram();

% Process fragment shader
if(~isempty(filename_fs))
    % The shader code in cell array (textfile2cellarray also removes
    % comment and empty lines, otherwise, shadercode will 
    % compile but does not work, escape character / ???)
    
    fsShader_mat = textfile2cellarray(filename_fs);

    % Conver matlab cell arrays with char arrays inside to String (arrays)
    fsShader = NET.createArray('System.String', length(fsShader_mat)); 
    for i=1:length(fsShader_mat), fsShader.Set(i-1, fsShader_mat{i}); end

    % Create shader id
    fragment_id = Gl.glCreateShader(Gl.GL_FRAGMENT_SHADER);

    % Specify shader source
    Gl.glShaderSource(fragment_id, fsShader.Length, fsShader, []);
    
    
    % Compile the shader code
    Gl.glCompileShader(fragment_id);
    
    % Get compiler errors and warnings
    errorBuffer= System.Text.StringBuilder;
    messageLength=NET.createArray('System.Int32', 1); 
    Gl.glGetShaderInfoLog(fragment_id,8192,messageLength,errorBuffer);
    messageLength=double(messageLength);
    if(messageLength>0)
            disp(errorBuffer.ToString)
            disp('The shader code');
            for i=1:length(fsShader_mat), disp([num2str(i) ' : '  fsShader_mat{i}]); end
    end
    
    
    % Attach shader to the program
    Gl.glAttachShader(program_id, fragment_id );
end

% Process vertex shader
if(~isempty(filename_vs))
    % The shader code in cell aray
    vsShader_mat =  textfile2cellarray(filename_vs);

    % Conver matlab cell arrays with char arrays inside to String (arrays)
    vsShader = NET.createArray('System.String', length(vsShader_mat)); 
    for i=1:length(vsShader_mat), vsShader.Set(i-1, vsShader_mat{i}); end

    % Create shader id
    vertex_id = Gl.glCreateShader(Gl.GL_VERTEX_SHADER);

    % Specify shader source
    Gl.glShaderSource(vertex_id, vsShader.Length, vsShader, []);

    % Compile the shader code
    Gl.glCompileShader(vertex_id);

    % Get compiler errors and warnings
    errorBuffer= System.Text.StringBuilder;
    messageLength=NET.createArray('System.Int32', 1); 
    Gl.glGetShaderInfoLog(vertex_id,8192,messageLength,errorBuffer);
    messageLength=double(messageLength);
    if(messageLength>0)
            disp(errorBuffer.ToString)
            disp('The shader code');
            for i=1:length(vsShader_mat), disp([num2str(i) ' : '  vsShader_mat{i}]); end
    end
    
    % Attach shader to the program
    Gl.glAttachShader(program_id, vertex_id);
end

% Links program object (create executable for GPU)
Gl.glLinkProgram(program_id);

% Validate Program
Gl.glValidateProgram(program_id);
succes=Gl.glGetProgramiv(program_id,Gl.GL_VALIDATE_STATUS);
pause(0.5);
Gl.glFinish();

if(succes==0)
   error('loadOpenGLShader:Shader', 'Program does not validate / execute');
end

function cellarray=textfile2cellarray(filename)
% Open text file
fid=fopen(filename,'r');
% Check if file can be read
if(fid<0), error('tloadOpenGLShader:textfile2cellary','shader file not found'); end
% cell array index
i=0;
% Loop through the lines
while true
    % Get text line
    tline = fgetl(fid);
    % Break if end of file reached
    if ~ischar(tline), break, end
    % Remove comment from shader code (important otherwise shader code
    % compiles, but will not work...???)
    c_pos=strfind(tline,'//');
    if(~isempty(c_pos))
        if(c_pos>1)
            tline=tline(1:c_pos-1);
        else
            tline=[];
        end
    end
    % Tabs to spaces
    tline(uint8(tline)==9)=' ';
    % Remove lines with only spaces
    if(nnz(tline==' ')==length(tline)), tline=[]; end
  
    % Add line to cell array if not empty
    if(~isempty(tline)), i=i+1; cellarray{i}=tline; end
end
% Close the text file
fclose(fid);