Android canvas path real-time performance

Question

I want to draw (4 or 5) real-time charts visualizing a lot of data (a new value every 30ms) within 15 minutes. I am using Path but it seems to work very slowly when I want to display over 20000 values and translate the canvas and it gets worse every second. I also tried using drawLine but it doesn't work fluently at all.

Does anyone have any ideas about a better solution than Path? Or maybe I am doing something wrong? My current solutio is : I initialize the Path in the beginning and then just add a new line to it every time I get a new value, then I translate the canvas.

Maybe someone has an idea why drawing a line and then translating the canvas is so slow that the break is visible and it doesn't work fluently? — beginner, Jul 04 '11 at 09:04

score 3 · Answer 1 · answered Jul 12 '11 at 19:07

Displaying a path of 20 000 values will probably be slow whatever you use, even in OpenGL, it's just a lot of data to send to the graphics chip to draw...

The "correct" way to do it (performance-wise) is probably to cache as much stuff as possible, and draw only what needs to be drawn. You could for example draw to a bitmap the first N points, and then only use a path for the next M points (and draw the bitmaps for the previous ones). Drawing a bitmap is pretty fast. So once in a while, you could just refresh your bitmap (which will take a bit more time) and then plot the remaining points.

You could also decide to have a shorter path : do you really need 20 000 values ? Couldn't you be grouping points 5 by 5 or 10 by ten (or even more) ? Currently, the screens are at most 1280 pixels wide anyways...

score 3 · Answer 2 · answered Sep 28 '11 at 08:06

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Are drawing all of that in every onDraw()? That's why it's slow. First of all, nobody can see changes every 30ms. So keep drawing updates into a cache bitmap, then call invalidate(). Then in onDraw() just copy that bitmap onto the canvas.

answered Sep 28 '11 at 08:06

Li_W

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Hi, a bit late to post here. But can you help me with your super idea, how to implement it? – zIronManBox Jun 27 '14 at 03:41

score 0 · Answer 3 · answered Jul 04 '11 at 08:39

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Drawing over 20000 lines with canvas is going to be slow, no matter what. My bet is that you have to go with openGL on this one. This link might be helpful: http://obviam.net/index.php/opengl-es-with-android-switching-from-canvas-to-opengl/

answered Jul 04 '11 at 08:39

Emir Kuljanin

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I would rather not use OpenGL, because I would have to rewrite almost everything. But if there is no other solution I will give it a try. – beginner Jul 04 '11 at 09:05

Android canvas path real-time performance

3 Answers3

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