Reduce memory use for textures in OpenGL ES 1.1

3
votes

My scene in OpenGL ES requires several large resolution textures, but they are grayscale, since I am using them just for masks. I need to reduce my memory use.

I have tried loading these textures with Bitmap.Config.ALPHA_8, and as RGB_565. ALPHA_8 seems to actually increase memory use.

Is there some way to get a texture loaded into OpenGL and have it use less than 16bits per pixel?

glCompressedTexImage2D looks like it might be promising, but from what I can tell, different phones offer different texture compression methods. Also, I don't know if the compression actually reduces memory use at runtime. Is the solution to store my textures in both ATITC and PVRTC formats? If so, how do I detect which format is supported by the device?

Thanks!

3
androidopengl-es

3 Answers

10
votes

PVRTC, ATITC, S3TC and so forth, the GPU native compressed texture should reduce memory usage and improve rendering performance.

For example (sorry in C, you can implement it as using GL11.glGetString in Java),

const char *extensions = glGetString(GL_EXTENSIONS);
int isPVRTCsupported = strstr(extensions, "GL_IMG_texture_compression_pvrtc") != 0;
int isATITCsupported = strstr(extensions, "GL_ATI_texture_compression_atitc") != 0;
int isS3TCsupported = strstr(extensions, "GL_EXT_texture_compression_s3tc") != 0;

if (isPVRTCsupportd) {
    /* load PVRTC texture using glCompressedTexImage2D */
} else if (isATITCsupported) {
...

Besides you can specify supported devices using texture format in AndroidManifest.xml.

EDIT:

2
votes

With Imagination Technologies-based (aka PowerVR) systems, you should be able to use PVRTC 4bpp and (depending on the texture and quality requirements) maybe even 2bpp PVRTC variant.

Also, though I'm not sure what is exposed in Android systems, the PVRTextool lists I8 (i.e. greyscale 8bpp) as target texture format, which would give you a lossless option.

1
votes

ETC1 texture compression is supported on all Android devices with Android 2.2 and up.