function demoColourCSF(COL_A,COL_B)

% Draws a colour variant of a Campbell-Robson CSF chart using a Bits++.

% -----------------------------------------------------------------------------

% This demonstration illustrates the use of the high bit depth drawing modes

% available on the Bits++ to display (a variant of) the Campbell-Robson

% Contrast Sensitivity Function chart. This particular demo uses the high

% bit depth Colour drawing mode. Another

% similar demonstration is available that uses the high resolution mono

% mode.

%

% USAGE: demoColourCSF(COLOUR1,COLOUR2);

%        demoColourCSF;

%

% EXAMPLE: demoColourCSF([0,0,1],[1,1,0])

%

% View the source code for this file for pointers on how to use the high bit

% depth colour drawing mode. Please note that the screen width will need to

% be doubled for this to work properly, as high bit depth colour uses two

% horizontally adjacent pixels in video memory for every one pixel output to

% the screen. For example, if you normally run an 800x600 Bits++ display, you

% now need to configure the 8:3 aspect ratio of 1600x600 for this video

% mode to work



% Please be aware that in this source description, some of the CSF chart

% parameters have been modified to improve its appearance on screen.

% Please do not rely on this file as a reference for how to produce a CSF

% chart.

%

% originally written by wp for Visage

% converted to Bits++ and OSX Psychtoolbox by ejw



if (nargin == 0)

    COL_A = [1,0,0];

    COL_B = [0,1,0];

else

    if (nargin ~= 2)

        error('USAGE: demoColourCSF(COLOUR1,COLOUR2) or demoColourCSF');

    end

end    



% Define screen

whichScreen=max(Screen('Screens'));



% Find the color values which correspond to white and black.  Though on OS

% X we currently only support true color and thus, for scalar color

% arguments,

% black is always 0 and white 255, this rule is not true on other platforms will

% not remain true on OS X after we add other color depth modes.  

white=WhiteIndex(whichScreen);

black=BlackIndex(whichScreen);

gray=GrayIndex(whichScreen);



% Open up the a window on the screen.

% This is done by calling the Screen function of the Psychophysics

% Toolbox. We need to open the onscreen window first, so that

% the offscreen storage allocated subsequently is properly

% matched to the onscreen frame buffer.

[window,screenRect] = Screen('OpenWindow',whichScreen,128,[],32,2);



% THE FOLLOWING STEP IS IMPORTANT.

% make sure the graphics card LUT is set to a linear ramp

% (else the encoded data will not be recognised by Bits++).

% There is a bug with the underlying OpenGL function, hence the scaling 0 to 255/256.  

% This demo will not work using a default gamma table in the graphics card,

% or even if you set the gamma to 1.0, due to this bug.

% This is NOT a bug with Psychtoolbox!

Screen('LoadNormalizedGammaTable',window,linspace(0,(255/256),256)'*ones(1,3));



% draw a gray background on front and back buffers

Screen('FillRect',window, gray);

Screen('Flip', window);

Screen('FillRect',window, gray);



% restore the Bits++ LUT to a linear ramp

linear_lut =  repmat(round(linspace(0, 2^16 -1, 256))', 1, 3);

BitsPlusSetClut(window,linear_lut);



% find out how big the window is

[POINTS_ACROSS, POINTS_DOWN]=Screen('WindowSize', window);



% ===========================

% DEFINE SPATIAL FREQUENCY GP

% ===========================

POINTS_ACROSS = POINTS_ACROSS / 2; % div by 2 for high res colour mode

SF_LOW        = 1.5;

SF_HIGH       = 300;

SF_BASE       = (SF_HIGH/SF_LOW) .^ (1/POINTS_ACROSS); % base

SF_POW        = [1:POINTS_ACROSS];                     % power

SF_FORM       = SF_BASE .^ SF_POW;                     % functional form

SF_MUL        = (SF_LOW/SF_BASE);                      % scaling factor

SF_VALU       = SF_FORM * SF_MUL;                      % values



% ==================

% DEFINE CONTRAST GP

% ==================

CT_LOW      = 1/1024;

CT_HIGH     = 1;

CT_BASE     = (CT_HIGH/CT_LOW) .^ (1/POINTS_DOWN); % base

CT_POW      = [1:POINTS_DOWN];                     % power

CT_FORM     = CT_BASE .^ CT_POW;                   % functional form

CT_MUL      = (CT_LOW/CT_BASE);                    % scaling factor

CT_VALU     = CT_FORM .* CT_MUL;                   % values



% ============================

% FORM IMAGE FROM PROGRESSIONS

% ============================

[XGRID,YGRID] = meshgrid(sin(SF_VALU),CT_VALU); % CT & SF are orthogonal

IMAGE         = XGRID .* YGRID;                 % contrast modulates amplitude

IMAGE         = (IMAGE + 1) / 2;                % map values to between 0 and 1.



% ===============

% COLOURISE IMAGE

% ===============

RANGE  = COL_A - COL_B;

OFFSET = COL_B;



RED_IMG   = (IMAGE.*RANGE(1)) + OFFSET(1);

GREEN_IMG = (IMAGE.*RANGE(2)) + OFFSET(2);

BLUE_IMG  = (IMAGE.*RANGE(3)) + OFFSET(3);



COLOUR_IMAGE = zeros(POINTS_DOWN, POINTS_ACROSS, 3);



COLOUR_IMAGE(:,:,1) = RED_IMG;

COLOUR_IMAGE(:,:,2) = GREEN_IMG;

COLOUR_IMAGE(:,:,3) = BLUE_IMG;



% ===============================================

% CODE NEEDED HERE !

% "COLOUR_IMAGE" should be corrected here for the

% inverse characteristic of the monitor.

% ===============================================



%don't decimate by 2 the number of horizontal pixels

SPACESCALE = 0;



%scale to the 0 to 2^16 range of Colour++

COLORSCALE = 1;



% encode the image in colour++ format

encoded_image = BitsPlusPackColorImage(COLOUR_IMAGE,SPACESCALE,COLORSCALE);

  

% put the csf chart image up on the back buffer

Screen('PutImage', window, encoded_image);



% make the make buffer current during the next blanking period

Screen(window,'Flip');



fprintf('Displaying CSF chart, hold a key to exit \n');



while(~KbCheck)

end;    



% if the system only has one screen, set the LUT in Bits++ to a linear ramp

% if the system has two or more screens, then blank the screen.

if (whichScreen == 0)

    % restore the Bits++ LUT to a linear ramp

    linear_lut =  repmat(round(linspace(0, 2^16 -1, 256))', 1, 3);

    BitsPlusSetClut(window,linear_lut);

    

    % draw a gray background on front and back buffers to clear out any old LUTs

    Screen('FillRect',window, gray);

    Screen('Flip', window);

    Screen('FillRect',window, gray);

    Screen('Flip', window);



    % Close the window.

    Screen('CloseAll');    

else

    % Blank the screen

    BitsPlusSetClut(window,zeros(256,3));



    % draw a black background on front and back buffers to clear out any old LUTs

    Screen('FillRect',window, black);

    Screen('Flip', window);

    Screen('FillRect',window, black);

    Screen('Flip', window);



    Screen('CloseAll');

end