Pixels from plot: getframe is too slow - image

Question

I need to do the following:
I have a fixed environment with a point in it
At each time step the point moves and I need to take a screenshot of the current status (environment + point)
What I do is
function getPixels(state)
fig = figure('visible','off')
hold all
plot_environment() % calls patch and other stuff
plot(state(1),state(2),'r+')
f = getframe();
data = f.cdata;
close(fig)
The problem is that it is very slow (0.6s which for me is really too much).
I tried using persistent fig and I can go down to 0.4s, still too much.
I read about using print or hardcopy, but it did not help. Even reducing the number of pixels by -r20 (1/5 of my default size) did not speed it up.
Any suggestion? Is there a faster way to get the pixels?
EDIT: ADDITIONAL DETAILS
The state is just a 2d point.
The environment is defined by some fixed known variables used to draw shapes. More specifically I have some points
points = [c11 c12
c21 c22
.....]
used to patch rectangles, circles and triangles. For this I use patch and circles.
So in the end I want to plot everything together and get the resulting pixels. Is there a way to do it without getframe or a way to speed it up?
COMPLETE EXAMPLE
It requires circles.
Launch tic, getPixels([0.1, 0.2]'); toc
It takes 0.43s on average. The getframe command alone takes 0.29s.
function data = getPixels(state)
fig = figure('visible','off');
hold all
c1 = [0.1 0.75;
0.45 0.75];
c2 = [0.45 0.4;
0.45 0.8];
radius = 0.1;
grey = [0.4,0.4,0.4];
% Circles
p = [c1; c2];
circles(p(:,1), p(:,2), radius, 'color', grey, 'edgecolor', grey)
% Rectangles
patch([0.1 0.45 0.45 0.1], [0.65 0.65 0.85 0.85], grey, 'EdgeAlpha', 0)
patch([0.35 0.55 0.55 0.35], [0.4 0.4 0.8 0.8], grey, 'EdgeAlpha', 0)
% Triangle
x = [0.95, 1.0, 1.0];
y = [1.0, 0.95, 1.0];
fill(x, y, 'r')
axis([0 1 0 1])
box on
axis square
% Point
plot(state(1),state(2),'ro','MarkerSize',8,'MarkerFaceColor','r');
f = getframe();
data = f.cdata;
close(fig)

Answer 1

You can reduce the execution time of Matlab's getframe() function by a factor of ten. The trick consists of not creating a figure each time you call the getPixels() function but using an existing one. You may pass the figure handle via the function parameters. And use the Matlab's function clf that clears the current figure window between two calls.
EDIT
Here is an example of the way I play with figure et getframe.
The following performance chart
is given by
%%
clear al
close all
clc
nbSim = 10 %number of getframe calls
tElapsed = zeros(nbSim, 2); %two types of getting frames
%% METHOD 1: figure within loop
for ind_sim = 1:nbSim
fig = figure;
%some graphical elements
hold all
patch(rand(1,4), rand(1,4), rand(1,3), 'EdgeAlpha', 0)
patch(rand(1,4), rand(1,4), rand(1,3), 'EdgeAlpha', 0)
fill(rand(1,3), rand(1,3), 'r')
plot(rand,rand,'ro','MarkerSize',8,'MarkerFaceColor','k');
%some axes properties
axis([0 1 0 1])
box on
axis square
tStart = tic;
f = getframe();
tElapsed(ind_sim,1) = toc(tStart);
data = f.cdata;
close(fig)
end
%% METHOD 2: figure outside loop
fig = figure;
for ind_sim = 1:nbSim
%some graphical elements
hold all
patch(rand(1,4), rand(1,4), rand(1,3), 'EdgeAlpha', 0)
patch(rand(1,4), rand(1,4), rand(1,3), 'EdgeAlpha', 0)
fill(rand(1,3), rand(1,3), 'r')
plot(rand,rand,'ro','MarkerSize',8,'MarkerFaceColor','k');
%some axes properties
axis([0 1 0 1])
box on
axis square
tStart = tic;
f = getframe();
tElapsed(ind_sim,2) = toc(tStart);
data = f.cdata;
clf
end
close(fig)
%% plot results
plot(tElapsed);
set(gca, 'YLim', [0 max(tElapsed(:))+0.1])
xlabel('Number of calls');
ylabel('Execution time');
legend({'within (method 1)';'outside (method 2)'});
title('GetFrame exectution time');
You have to drop the creation of a figure, even if it is declared not visible. This impairs the execution times.