我的Galaxy S4屏幕边缘点精灵消失（不在Nexus 7上）

Question

I am experimenting with a particle emitter based on this code: https://code.google.com/p/sravan-work/source/browse/trunk/OpenGL+ES2/es2particles/src/es2/learning/ParticleRenderer.java

Currently, the particle emitter works great on my Nexus 7; the point sprites are generated in the center of the screen and either 1) fade out or 2) fly past the edge of the screen.

Unfortunately, on my Galaxy S4, the point sprites disappear from the display as soon as their mid-point reaches the edge of the screen. This causes a really unpleasant visual effect.

Both devices are running Android 4.3

Question : Why is it that the sprites will glide off the screen on the (Asus) Nexus 7, but on the Galaxy S4 they suddenly disappear ? Is there anything that can be done to prevent the sudden disappearance ?

Additional notes:

For the Galaxy S4 the following is printed in logcat:

12-03 00:29:15.288: I/Adreno-EGL(31137): <qeglDrvAPI_eglInitialize:316>: EGL 1.4 QUALCOMM build:  (CL4169980) 
12-03 00:29:15.288: I/Adreno-EGL(31137): OpenGL ES Shader Compiler Version: 17.01.10.SPL 
12-03 00:29:15.288: I/Adreno-EGL(31137): Build Date: 09/26/13 Thu

For the Nexus 7, the following is printed in logcat:

12-03 00:14:38.144: D/libEGL(25303): loaded /system/lib/egl/libEGL_tegra.so
12-03 00:14:38.154: D/libEGL(25303): loaded /system/lib/egl/libGLESv1_CM_tegra.so
12-03 00:14:38.174: D/libEGL(25303): loaded /system/lib/egl/libGLESv2_tegra.so
12-03 00:14:38.194: D/OpenGLRenderer(25303): Enabling debug mode 0

Answer 1

The sprites are based on a single point in their centre, around which a texture is drawn. If this point goes outside the rendering area, they are clipped, since their entire geometry is technically outside the view.

There might be a few workarounds to avoid the sudden dissapearance:

1. Manually fade the sprites as they approach the edge of the screen.
2. Extend the view/render area so that it goes "outside" the screen (not sure if this is possible).
3. Use squares with four vertices instead of sprites (as long as a vertex is on screen, the related triangles are not clipped)

For option 3:
First you will have to define a square instead of a single point per particle:

float verts[] = {-1, 1, 0,  1, 1, 0,  1,-1, 0,  -1,-1, 0};

Depending on how you want your particles to behave, you could remove the third coordinate of each vertex and set it to an appropriate value in the vertex shader too.

Second, instead of drawing GLES20.GL_POINTS , you will have to draw triangles, with the array I posted, GLES20.GL_TRIANGLE_FAN will create a square.

You will also have to set the position and size of the particle in the vertex shader. Something like this a_Position*size*0.5 + translate should do the trick. You can of course avoid the halving of the size if you either use smaller sizes or make the vertex values smaller in the verts[] array. translate would be the calculated position of the particle.

Note1: remember that glPointSize sets the size in pixels, but in this example the size is in world-space units. A size of 10 would probably be larger than the screen in this example

Note2: since you are using actual geometry instead of points now, you can use a perspective matrix to make particles that are further away appear smaller.