CODEWITHSUNDEEP
androidmobileopengl-es3dtablet
Kilian Perdomo Curbelo
Kilian Perdomo Curbelo

Reputation: 1348

Opengl texture flickering in some android devices

We are a team of developers working on a terrain visualization software over a virtual 3D globe. The project is aimed at mobile devices running android, mainly tablets and mobile phones. We have tested this in several devices and, while mobile phones seem to run the application fine (we haven't detected any issues on any of them), some tablets seem to have problems when drawing the textures in the screen.

For clarity purposes, im attaching a video that displays the problem, since its a little difficult to explain with words. This example shows a sphere divided in 200 sectors, each one with a different texture.

Texture problem video

As you can see, sometimes it looks like it is trying to draw two different textures in the same sector at the same time.

We have tested this in these devices:

Im posting the critical code that may be involved in this. First the fragment shader that is used to draw the textures:

varying mediump vec2 TextureCoordOut;
uniform sampler2D Sampler;
....
gl_FragColor = texture2D (Sampler, TextureCoordOut);

Next, im posting the key instructions that are executed in OpenGL, since the code is spared in several big functions:

GLES20.glGenTextures(num, idTextures, 1);  //declare 200 textures
...
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, idTextures[texture]); //texture binding
...
GLES20.glVertexAttribPointer(Attributes.Position, size, GLES20.GL_FLOAT, false, stride, fb);
...
GLES20.glVertexAttribPointer(Attributes.TextureCoord, size, GLES20.GL_FLOAT, false, stride, fb);
...
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, first, count);

Im sorry not to be able to provide more details, but after several weeks of debugging, we have no clue at all of what could be causing this. Im turning to you hoping for any leads, since we are completely lost right now. Thanks in advance.

Upvotes: 3

Views: 3008

Answers (1)

HardCoder
HardCoder

Reputation: 3036

I think I might know what causes you difficulties. The only devices where it doesn't work for you are Tegra 2 devices. I recently started working with a Tegra 2 device and noticed certain differences. Compared to other devices Nvidia seems to have introduced certain kinds of rounding errors where some things can behave differently from other GPUs. I had to go to extreme lengths and use workarounds to get it working the way I want with my complex shaders.

And what I could see on your video looks sort of like the z-buffer might not have enough resolution and that causes some kind of z-fighting: http://en.wikipedia.org/wiki/Z-fighting. I am not sure because I don't really see from your code/description if you are drawing triangles that are very close together and can cause this kind of behaviour in the z-buffer.

But maybe you can try to scale the vertices (x,y,z) somewhat up or down and see what happens to the flickering. If it changes it probably has something to do with that, if not, the problem might have another reason, but then a little more code would be nice.

It would also be interesting to try to narrow it down by not painting the whole sphere but just one or two triangles where the problem occurs and see if it still happens.

PS: A longer video would have been better, short clips suck on vimeo.

Upvotes: 2

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