Callbacks in matlab - matlab

Question

I have an user interactive animation in matlab where a shape is translated and rotates across a plot and the user has to click on it. If they click on it, their score is incremented and if not, the animation stops. For some reason the program does not seem to be registering the clicks from the user and I am unsure why. I have posted the code below. Any help would be greatly appreciated.
Animation Function:
function movingPolygon
global gUserHitPolygon;
global gCurrentXVertices;
global gCurrentYVertices;
gUserHitPolygon = true;
global gScore;
nSides =4;
%Polar points
r=1;
theta = pi/nSides * (1:2:2*nSides-1);
%Cartesisn points
x0 = r * cos(theta);
y0 = r * sin(theta);
nFrames = 100;
xx = linspace(0,10, nFrames);
yy = xx;
rr = linspace(0, 2*pi, nFrames);
h = figure;
set(h,'WindowButtonDownFcn', #mouseDownCallback);
i=1;
while gUserHitPolygon
rX = [cos(rr(i)), -sin(rr(i))];
rY = [sin(rr(i)), cos(rr(i))];
x1 = rX * [x0; y0];
y1 = rY * [x0; y0];
x2= x1 + xx(i);
y2= y1 + yy(i);
gCurrentXVertices=x2;
gCurrentYVertices=y2;
y=fill(x2, y2, 'b');
xlim([0,10]); ylim([0,10]);
hold on;
pause(0.000000003);
delete(y);
title(sprintf('Score: %d', gScore));
i=i+1;
if i>nFrames
i=1;
end
end
end
Callback Function
function mouseDownCallback(~,~)
global gUserHitPolygon;
global gCurrentXVertices;
global gCurrentYVertices;
global gScore;
gScore=0;
xVertices = gCurrentXVertices;
yVertices = gCurrentYVertices;
% if we have valid (so non-empty) sets of x- and y-vertices then...
if isempty(xVertices) && isempty(yVertices)
% get the coordinate on the current axis
coordinates = get(gca,'CurrentPoint');
coordinates = coordinates(1,1:2);
% if the coordinate is not in the polygon, then change the
% flag
if inpolygon(coordinates(1),coordinates(2),xVertices,yVertices)
gUserHitPolygon = false;
else
gScore=gScore+1;
end
end
end

Answer 1

I found 3 issues with your code.
First, you initialise the value of gScore as 0 inside the callback function. That means that every time the mouse is clicked, gScore is set to 0. Instead, initialise it to 0 in the main function, just after you define it as a global variable, and just call global gScore in the callback.
Secondly, you are using an if statement to determine whether you have a valid set of coordinates from the click, and if so, you want to execute some code. However, your if statement is testing whether the inputs are empty, and only if they are is it running. Change the if statement to
if ~isempty(xVertices) && ~isempty(yVertices)
which will evaluate to 1 if you have valid (non-empty) inputs.
Thirdly, your test for whether the user clicks inside or outside the polygon has the same problem. If the user clicks inside the polygon, inpolygon will be true, and so you will execute gUserHitPolygon = false;, rather than the intended gScore=gScore+1;. To fix this, again, negate your condition:
if ~inpolygon(coordinates(1),coordinates(2),xVertices,yVertices)