GL Maximum Textures Size Policy

Question

I'm developing a game with AndEngine. Since I'm doing it for Android and I want to cover as many devices as possible without the textures quality trade off I have 2 texture packs types: the HD and the LOW:

• HD textures = 2048x2048
• LOW textures= 1024x1024
• HD camera = 800x1280
• LOW camera = 400x640

I've have made all the logic of setting up a HD texture pack or a LOW texture pack, what I need now is a good policy for choosing witch to use when the app starts up.

Using AndEngine's:

GLState state = new GLState();
int max = state.getInteger(GLES20.GL_MAX_...);

I came across some values:

Model: Samsung Note 8, Sony XPERIA U
GL_MAX_TEXTURE_SIZE: 4096
GL_MAX_TEXTURE_IMAGE_UNITS: 8
GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS: 8

Model: Samsung Galaxy Mini, Samsung S3 Mini, HTC One S
GL_MAX_TEXTURE_SIZE: 4096
GL_MAX_TEXTURE_IMAGE_UNITS: 16
GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS: 20

Model: Samsung S4, Nexus4, XPERIA Z1
GL_MAX_TEXTURE_SIZE: 4096
GL_MAX_TEXTURE_IMAGE_UNITS: 16
GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS: 32

In this openGL Docs I could find each constant meaning, but I'm a little lost here, I don't know how to use this data in order to choose the right setup for my textures and camera.

I need your help and tips, am I in the right path? What should I do next with this info?
Thanks for your time.

Answer 1

GL_MAX_TEXTURE_SIZE is the maximum square texture dimensions your hardware supports.

• Neither the X nor Y dimensions of any texture can exceed this size.

GL_MAX_TEXTURE_IMAGE_UNITS refers to the maximum number of textures (e.g. unique sampler uniform names in a GLSL program) you can bind and use in the programmable pipeline (GL_MAX_TEXTURE_UNITS is the fixed-function analog in GLES 1.0).

• In GLES 2.0 this has a minimum value of 2.

GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS refers to the number of textures you can use across all shaders in your GLSL program.

• 4 samplers in a fragment shader + 4 samplers in a vertex shader = 8 Combined Texture Image Units

NOTE: OpenGL ES 2.0 does not require texture lookup support in vertex shaders, and I suspect Samsung Note 8, Sony XPERIA U has an implementation that does not support this, judging by the parity between COMBINED and general TMU counts.

• Querying the value of GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS would put an end to any speculation though.

---

To answer your actual question, though... the only one of these values you can use to determine which texture pack to use is GL_MAX_TEXTURE_SIZE. There is no OpenGL parameter you can query to determine the underlying hardware's memory capacity / texture fillrate, which is what you really want to know when selecting texture packs. You will need to gather this information through other means, perhaps a mini-benchmark or a database of known hardware, or if you are lucky the platform has a separate API that lets you query this.

Answer 2

I came across another test case that may come in handy, checking for available memory:

        ActivityManager.MemoryInfo mi = new ActivityManager.MemoryInfo();
        ActivityManager activityManager = (ActivityManager) context.getSystemService(context.ACTIVITY_SERVICE);
        activityManager.getMemoryInfo(mi);
        long availableMegs = mi.availMem / 1048576L;

So far my test cases are:

if (IS_TABLET7 || IS_TABLET10) {
    useHIGH &= smallestWidthSize >= TABLET_MAX_SMALLEST_WIDTH;
} else {
    useHIGH &= smallestWidthSize >= SMARTPHONE_MAX_SMALLEST_WIDTH;
}

Log.i(C.TAG, "=========SCREEN DIMENSIONS=========");
Log.i(C.TAG, "Screen Size Info: smallestWidthSize = " + smallestWidthSize);
Log.i(C.TAG, "Screen Size Info: smallestWidthSize >= MAX_SMALLEST_WIDTH (" + (IS_TABLET ? TABLET_MAX_SMALLEST_WIDTH : SMARTPHONE_MAX_SMALLEST_WIDTH) + ")? " + useHIGH);
Log.i(C.TAG, "Screen Size Info: should use Texture Type > " + (useHIGH ? "HIGH" : "LOW"));


useHIGH &= availableMegs > MIN_RAM_LIMIT;
Log.i(C.TAG, "=========AVAILABLE RAM=========");
Log.i(C.TAG, "Memory Info: available RAM = " + availableMegs + "Mb");
Log.i(C.TAG, "Memory Info: available RAM > MIN_RAM_LIMIT(" + MIN_RAM_LIMIT + "Mb)? " + useHIGH);
Log.i(C.TAG, "Memory Info: should use Texture Type > " + (useHIGH ? "HIGH" : "LOW"));

As stated above I'll always keep this post updated until a good solid solution is reached.