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function handle = LoadShaderFromFile(filename, shadertype, debug)
% handle = LoadShaderFromFile(filename [, shadertype] [, debug])
%
% Loads a GLSL OpenGL shader definition from textfile 'filename' and
% creates an OpenGL GLSL shader of type 'shadertype'. Returns a handle to
% the new shader. If shadertype is omitted, the type of the shader is
% derived from the filename extension: .vert == GL_VERTEX_SHADER, .frag ==
% GL_FRAGMENT_SHADER, .geom == GL_GEOMETRY_SHADER, .tesscontrol =
% GL_TESS_CONTROL_SHADER, .tesseval = GL_TESS_EVALUATION_SHADER. The
% optional 'debug' flag allows to enable debugging output.
%
% On successfull load & creation, a 'handle' to the new shader is returned.
%
% 29-Mar-2006 written by MK
% 29-Jul-2009 Bugfixes by MK: debug must default to 1, not 2!
% 06-Sep-2013 Add geometry shader and tesselation shader support. (MK)
global GL;
if isempty(GL)
InitializeMatlabOpenGL([],[],1);
end;
% Make sure we run on a GLSL capable system.
AssertGLSL;
if nargin < 3
debug = 1;
end;
if nargin < 1
filename = [];
end
if isempty(filename)
% Set default shader file name:
error('LoadShaderFromFile() called without any shader filename!');
end;
% Add path to our own shader directory if no path given:
if isempty(fileparts(filename))
% No path to the shader defined as part of the filename. Add our
% default path to our standard shader directory:
filename = [ PsychtoolboxRoot 'PsychOpenGL/PsychGLSLShaders/' filename ];
end;
if nargin < 2
shadertype = [];
end
if isempty(shadertype)
% Try to autodetect shadertype from file extension:
if ~isempty(strfind(filename, '.frag'))
shadertype = GL.FRAGMENT_SHADER;
if debug>0, fprintf('Building a fragment shader:'); end;
elseif ~isempty(strfind(filename, '.vert'))
shadertype = GL.VERTEX_SHADER;
if debug>0, fprintf('Building a vertex shader:'); end;
elseif ~isempty(strfind(filename, '.geom'))
shadertype = GL.GEOMETRY_SHADER;
if debug>0, fprintf('Building a geometry shader:'); end;
elseif ~isempty(strfind(filename, '.tesscontrol'))
shadertype = GL.TESS_CONTROL_SHADER;
if debug>0, fprintf('Building a tesselation control shader:'); end;
elseif ~isempty(strfind(filename, '.tesseval'))
shadertype = GL.TESS_EVALUATION_SHADER;
if debug>0, fprintf('Building a tesselation evaluation shader:'); end;
else
error('No shadertype provided and could not derive type from filename extension!');
end;
end;
if debug>0
fprintf('Reading shader from file %s ...\n', filename);
end;
% Read shader source code from file:
[fid errmsg]=fopen(filename, 'rt');
if fid<0
error('Could not open shader definition file %s [%s]!', filename, errmsg);
end;
shadersrc = fread(fid);
fclose(fid);
% Create shader, assign sourcecode and compile it:
handle = glCreateShader(shadertype);
if handle <= 0
fprintf('The handle created by glCreateShader is %i -- An invalid handle!\n', handle);
error('LoadShaderFromFile: glCreateShader failed to create a valid shader! Something is wrong with your graphics drivers!');
end
if debug > 1
glShaderSource(handle, shadersrc, debug);
else
glShaderSource(handle, shadersrc);
end;
glCompileShader(handle);
% Done.
return;
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