Using method -canvas.drawBitmap(bitmap, src, dst,

问题:

Everytime I use this code nothing is drawn. I need to draw a bitmap inside of a specified rectangle.

canvas.drawBitmap(MyBitmap, null, rectangle, null)

I've looked online but can't find much help.

回答1:

EDIT

---

The original answer is incorrect. You can use the sourceRect to specify a part of a Bitmap to draw. It may be null, in which case the whole image will be used.

As per the fryer comment he was drawing beneath something, I'll add a note on that.

drawBitmap(bitmap, srcRect, destRect, paint) does not handle Z ordering (depth) and the order of calling draw on object matters.

If you have 3 shapes to be drawn, square, triangle and circle. If you want the square to be on top then it must be drawn last.

---

You're not specified any source, so its not drawn anything.

Example:

You have a Bitmap 100x100 pixels. You want to draw the whole Bitmap.

canvas.drawBitmap(MyBitmap, new Rect(0,0,100,100), rectangle, null);

You want to draw only the left half of the bitmap.

canvas.drawBitmap(MyBitmap, new Rect(0,0,50,100), rectangle, null);

You need to specify the source rect, the source rect can be a rectangle anywhere from 0,0 to the width,height of the bitmap.

回答2:

The main item to remember when defining the Rect is:

• left < right and top < bottom

The rect is in screen coordinates (positive Y downward) ...

I find it helpful to think of the Rect arguments

(left, top, right, bottom)

as

(X, Y, X + Width, Y + Height)

where X,Y is the top left corner of the sprite image.

NOTE: If want to center the image on a particular location, remember to offset those values by half the sprite width & height. For example:

int halfWidth = Width/2;
int halfHeight = Height/2
Rect dstRectForRender = new Rect( X - halfWidth, Y - halfHeight, X + halfWidth, Y + halfHeight );
canvas.drawBitmap ( someBitmap, null, dstRectForRender, null );

This uses the whole original image (since src rect is null) and scales it to fit the size and position from dstRectForRender ... and using the default Paint.

回答3:

I dont know why but this worked for me!

Rect rectangle = new Rect(0,0,100,100);
canvas.drawBitmap(bitmap, null, rectangle, null);

Thanks:)