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function [devid, dev] = PsychGetCamIdForSpec(className, inputNameOrPort, instance, engineId)
% Return deviceIndex of a specified camera, one that matches given criteria.
%
% [deviceIndex, dev] = PsychGetCamIdForSpec([className][, inputNameOrPort][, instance][, engineId]);
%
% Searches for video sources which match given criteria. A handle to the
% first source that satisfies the criteria is returned in argument
% 'deviceIndex' - You can open a connection to the source via
% Screen('OpenVideoCapture', windowPtr, deviceIndex, ...);
%
% The 2nd optional return argument contains the complete 'dev'ice
% description struct, as returned by Screen().
%
% Returns empty variables if no match can be made.
%
% Optional criteria:
%
% 'className' Index or name of video input device class: Default is to
% accept any class. This matches against the 'ClassName' property of the
% list returned by Screen('VideoCaptureDevices').
%
% 'inputNameOrPort' selects the i'th input device of a matching class if an
% index is given (zero-based), or a specific named device, e.g., 'iSight'
% for the builtin iSight camera of Apple hardware.
%
% 'instance' If multiple devices match, take the i'th device where i ==
% instance. By default, the first device (instance == 0) is assigned.
%
% 'engineId' Enumerate for video capture engine 'engineId'. By default, the
% default videocapture engine is used.
%
%
% History:
% 9.5.2009 mk Written.
if nargin < 1
className = [];
end
if nargin < 2
inputNameOrPort = [];
end
if nargin < 3
instance = [];
end
if isempty(instance)
instance = 0;
end
if nargin < 4
engineId = [];
end
cams = Screen('VideoCaptureDevices', engineId);
devid = [];
dev = [];
curinst = -1;
for i=1:length(cams)
if ~isempty(className)
if isnumeric(className)
if cams(i).ClassIndex ~= className
% ClassIndex doesn't match: Reject.
continue;
end
else
if isempty(strfind(cams(i).ClassName, className))
% Classname doesn't match: Reject.
continue;
end
end
end
if ~isempty(inputNameOrPort)
if isnumeric(inputNameOrPort)
if cams(i).InputIndex ~= inputNameOrPort
% InputIndex doesn't match: Reject.
continue;
end
else
if isfield(cams(i), 'InputName') && isempty(strfind(cams(i).InputName, inputNameOrPort))
% InputName doesn't match: Reject.
continue;
end
if isfield(cams(i), 'DeviceName') && isempty(strfind(cams(i).DeviceName, inputNameOrPort))
% InputName doesn't match: Reject.
continue;
end
end
end
% Matching criteria satisfied. Matching instance?
curinst = curinst + 1;
if curinst == instance
% Assign deviceIndex for matched device:
devid = cams(i).DeviceIndex;
dev = cams(i);
break;
end
end
% Ok, either devid is empty if no matching device could be found, or we
% have a unique deviceIndex for use with Screen('OpenVideoCapture').
return;
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