# Use OpenGL display Image (v) Add mobile

Source: Internet
Author: User

Written by: Jdneo-Original: http://developer.android.com/training/graphics/opengl/motion.html

Ext.: http://hukai.me/android-training-course-in-chinese/graphics/opengl/motion.html

Drawing graphics on the screen is a basic feature of OpenGL, and of course we can do these things with other Android graphics framework classes, including canvas and drawable objects. What's special about OpenGL es is that it also provides other features, such as moving and transforming drawing graphics in three-dimensional space, or creating compelling user experiences in other unique ways.

Rotate a shape

Using OpenGL ES 2.0 to rotate a drawing graph is relatively straightforward. In the renderer, create another transformation matrix (a rotation matrix) and combine it with our projection transformation matrix and camera view transformation matrix:

``Privatefloat[] Mrotationmatrix =Newfloat[16];PublicvoidOndrawframe(GL10 GL) {float[] Scratch =Newfloat[16]; ...Create a rotation transformation for the trianglelong time = Systemclock.uptimemillis ()% 4000l; float angle = 0.090f * ((int) time); Matrix.setrotatem (Mrotationmatrix, 0, Angle, 0, 0,-1.0f); //Combine the rotation matrix with the projection and camera view  Note that the Mmvpmatrix factor *must is first* in order //for the matrix multiplication PR Oduct to be correct. Matrix.multiplymm (Scratch, 0, Mmvpmatrix, 0, MRotationMatrix, Span class= "Hljs-number" >0); //Draw triangle Mtriangle.draw (scratch);}        ``

If your triangle is still not rotated after you have completed these changes, verify that you have commented out the code that corresponds to the configuration that enabled Glsurfaceview.rendermode_when_dirty, and that knowledge will be expanded in the next section.

Enable continuous rendering

If you follow the example code of this lesson in strict accordance with this step, then make sure that the line of code that sets the rendering mode is `RENDERMODE_WHEN_DIRTY` commented, otherwise OpenGL will only perform a single rotation on the shape, It then waits for the Glsurfaceview container's Requestrender ()) method to be called before the render operation continues.

``public MyGLSurfaceView(Context context) {    ...    // Render the view only when there is a change in the drawing data. // To allow the triangle to rotate automatically, this line is commented out: //setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);}``

Unless an object has a change that is unrelated to the user's interaction, it is generally recommended that this configuration be opened. The content in the next lesson will release this comment and set this configuration option again.

(GO) Use OpenGL display image (v) Add mobile

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