How do you find out the scale of an graphics matrix in Android

android graphics vector-graphics
OverclockedTim picture OverclockedTim · Mar 4, 2011 · Viewed 10k times · Source

So, it appears to be fairly easy to do pinch zoom in android - but I would also like to be able to snap back the image when it goes out of bounds, and to do that the most reasonable thing seems to be to do things like when the scale < 1, rescale to 1. However, I can't seem to find a good way to retrieve the scale from the the graphics matrix.

One possible solution might be to map a point using the matrix's mapPoints function and see where it ends up, but in addition to being trickly, that just feels ugly and indirect to me. Are there any better solutions for retrieving the scale from an Android graphics matrix?

Answer

Henrik picture Henrik · Mar 31, 2011 
float[] f = new float[9];
matrix.getValues(f);

float scaleX = f[Matrix.MSCALE_X];
float scaleY = f[Matrix.MSCALE_Y];

will probably be what you are looking for. the values given will be as followed:

0 : Scale X

1 : Skew X

2 : Translate X

3 : Scale Y

4 : Skew Y

5 : Translate Y

6 : Perspective 0

7 : Perspective 1

8 : Perspective 2

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