Android: Drawing to canvas, way to make bottom lef

问题:

I'm trying to write a graph class I can use in Android(I'm aware pre-made ones exist), but converting all of my coordinates would be a pain. Is there an easy way to make the screen coordinates start at the bottom left?

回答1:

No, I don't know of a way to move 0,0 to the bottom left and get what you would typically think of as "normal" coordinates.

But combining scale() and translate() might do the trick to achieve the same effect.

canvas.translate(0,canvas.getHeight());   // reset where 0,0 is located
canvas.scale(1,-1);    // invert

回答2:

You can flip your Canvas with something like canvas.scale(1, -1) and then translate it to the right place.

回答3:

You can use canvas.translate() http://developer.android.com/reference/android/graphics/Canvas.html#translate(float, float) to move the origin to where you want.

回答4:

The android canvas has the origin at the top left. You want to translate this to the bottom right. To do this translation, subtract the y co-ordinate from the Canvas height.

float X1 = xStart;
float Y1 = canvas.getHeight() - yStart;  //canvas is a Canvas object
float X2 = xEnd;
float Y2 = canvas.getHeight() - yEnd;
canvas.drawLine(X1, Y1, X2, Y2, paint ); //paint is a Paint object

This should make your line start from the bottom left.