Android development: Create a thread on surfaceview to draw a rotating image and refresh a specific area (dirty rectangle)

What is a dirty rectangle? For example, when you draw a rotating image on surfaceview, you only need to refresh a specific rectangular area. This rectangle is a dirty rectangle. On surfaceview, canvas = holder. lockcanvas (New rect (0, 0,130,130); // obtain the dirty rectangle refresh of the canvas, such as the rect parameter.

Please refer to the source code:

Package Yan. guoqi. rectphoto; import android. content. context; import android. graphics. bitmap; import android. graphics. bitmapfactory; import android. graphics. canvas; import android. graphics. matrix; import android. graphics. paint; import android. graphics. pixelformat; import android. graphics. rect; import android. util. attributeset; import android. util. log; import android. view. surfaceholder; import android. view. surfaceview; public class drawsurfaceview extends surfaceview implements surfaceholder. callback {Private Static final string tag2 = "drawsv"; private Boolean runflag = true; protected surfaceholder holder; private bitmap rotateimg; private thread mythread; Public drawsurfaceview (context, attributeset attrs) // constructor {super (context, attrs); // todo auto-generated constructor stubrotateimg = bitmapfactory. decoderesource (getresources (), R. drawable. rotate_circle); rotateimg = bitmap. createscaledbitmap (rotateimg, 100,100, true); holder = This. getholder (); holder. addcallback (this); holder. setformat (pixelformat. transparent); // top-layer surfaceview rendering to transparent this. setzorderontop (true); mythread = new thread (New mythread ();} public void surfacechanged (surfaceholder arg0, int arg1, int arg2, int arg3) {// todo auto-generated method stublog. V (tag2, "drawsv: surfacechanged... ");} public void surfacecreated (surfaceholder arg0) {// todo auto-generated method stublog. V (tag2, "drawsv: surfacecreated... "); // start the custom thread mythread. start ();} public void surfacedestroyed (surfaceholder arg0) {// todo auto-generated method stublog. V (tag2, "drawsv: surfacedestroyed... "); // terminate the custom thread runflag = false; mythread. interrupt ();}/* Custom thread */class mythread implements runnable {public void run () {// todo auto-generated method stubcanvas canvas = NULL; int rotate = 0; while (runflag) {try {canvas = holder. lockcanvas (New rect (0, 0,130,130); // obtain the canvas paint = new paint (); // canvas. drawbitmap (rotateimg, 0, 0, paint); // draws the rotating background // creates a matrix to control image rotation and shifts the matrix = new matrix (); // sets the Rotation Angle matrix. postrotate (rotate + = 48) % 360, rotateimg. getwidth ()/2, rotateimg. getheight ()/2); // set the left margin and top margin of matrix. posttranslate (0, 0); // draw a rotated image canvas. drawbitmap (rotateimg, matrix, paint); // sleep controls the maximum frame rate to draw 30 threads three times per second. sleep (30); holder. unlockcanvasandpost (canvas); // unlock the canvas and submit the painted image} catch (exception e) {// todo: handle exceptionlog. V (tag2, "drawsurfaceview: painting failed... ");}}}}}

Notes:

The first is how to safely stop a thread. Set the flag here. Because the built-in stop () method is not secure, Android itself is not recommended. For details about how to safely abort a thread, refer to here: http://www.iteye.com/problems/67052 http://www.dewen.org/q/1957

Second, Holder. unlockcanvasandpost (canvas); // unlock the canvas and submit the painted image. lockcanvas (New rect (0, 0,130,130); // obtain the canvas in. For example. The reason is that the canvas cannot be unlocked when the thread is suspended.

Third, use the Matrix to rotate the image's core code:

// Create a matrix to control image rotation and smooth matrix = new matrix (); // set the Rotation Angle matrix. postrotate (rotate + = 48) % 360, rotateimg. getwidth ()/2, rotateimg. getheight ()/2); // set the left margin and top margin of matrix. posttranslate (0, 0); // draw a rotated image canvas. drawbitmap (rotateimg, matrix, paint); // sleep controls the maximum frame rate to draw 30 threads three times per second. sleep (30 );

Fourth, the reason why surfaceview is set to the top-level transparency is that when the miscellaneous want to explore the bottom-layer surfaceview to preview the camera video, draw a rotating image animation on the top-level surfaceview. Unfortunately, the image is indeed rotated, and the underlying camera preview is normal. However, a rotating image blocks the preview image.Alas, it seems that
The image I rotate is not transparent ???