How to update / animate a complicated figure in MATLAB? - matlab

Question

I need to animate a complex figure consisting of a chain of rectangles, forming an arm.
Here is an example of how this arm looks like when not animated :
To animate this figure, I made the following code :
function renderFrame(fig, data)
hold(ax, 'on'); % Need to hold so that new elements of the arm add themselves
showMembers(fig, data); % Create patches and rotate them to the right angle to create members
showJoints(fig, data); % Draw circles at the joints betwwen the members. Use the width of rectangle members
drawnow;
hold(ax, 'off'); % Next rendering will replace this one; No need to hold
end
function rotateMember(fig, data, iMember, rotAngle)
for iAngle = 1:rotAngle
updateMemberAngle(data, i, 1); % Change thew data so the i-th member rotates by 1
renderFrame(fig); % Show frame after the data was changed
end
end
function main()
fig = figure;
ax = gca;
axis(ax, 'equal');
setAxis(data); % Set axis limits and create axis arrows with totalLength of the arm
renderFrame(ax, data);
rotateMember(fig, data, 3, 90); % Rotate 3rd member by 90 degrees
end
main()
But the frames of my animation doesn't clear at all. It results in this figure :
What am I doing wrong ? Is there a way to plot complicated figures with multiple parts and to animate it, by clearing frame ?
I looked into using newplot and nextplot, but MATLAB's documentation on the subject is incomplete, as always. I also tried creating graphic objects and then setting the data at each iteration, but it rejects an exception every time the figure is deleted since "graphics objects are deleted".

Answer 1

It seems to me as if in your approach, you're not erasing the plot when drawing the next frame. Maybe calling cla() prior to drawing the next frame would make it work? However, this may produce a flickering behavior if the redrawing is done in the wrong order.
I suggest taking a look at animation techniques in Matlab to see three different ways to produce animations.

Answer 2

Found a way to clear the axis childrens, except the two axis quivers (arrows).
Here is a code that works properly:
function renderFrame(renderAxes, data)
% CHECK IF THERE ARE MORE GRAPHIC OBJECTS THAN ONLY THE QUIVERS
if ~(length(renderAxes.Children) == 2)
% DELETE EVERYTHING EXCEPT THE AXIS QUIVERS THAT WERE RENDERED AT THE BEGINNING
% MATLAB ADDS NEW GRAPHIC OBJECTS TO THE BEGINNING OF AX.CHILDREN
delete(renderAxes.Children(1:length(renderAxes.Children)-2))
end
showMembers(renderAxes, data); % Create patches and rotate them to the right angle to create members
showJoints(renderAxes, data); % Draw circles at the joints betwwen the members. Use the width of rectangle members
drawnow;
end
function rotateMember(ax, data, iMember, rotAngle)
for iAngle = 1:rotAngle
updateMemberAngle(data, i, 1); % Change thew data so the i-th member rotates by 1
renderFrame(ax, data); % Show frame after the data was changed
end
end
function main()
fig = figure;
ax = gca;
axis(ax, 'equal');
% HOLD AXES AT THE BEGINNING OF THE SCRIPT
hold(ax, 'on');
setAxis(data); % Set axis limits and create axis arrows with totalLength of the arm
renderFrame(ax, data);
rotateMember(ax, data, 3, 90); % Rotate 3rd member by 90 degrees
end
main()