GLSLCompat.glsllib doesn't compile on Android

[nickidebruyn]

While test jme3.7.0 with my android projects I found that the jme3-core/src/main/resources/Common/ShaderLib/GLSLCompat.glsllib
code contains ';' semicolons at the end of the first few lines and android is not happy with that.

Error I am experiencing:

ERROR: 0:11: ';' : Syntax error:  syntax error
INTERNAL ERROR: no main() function!
ERROR: 1 compilation errors.  No code generated.                                                                                                    
                                                                                                    	at com.jme3.renderer.opengl.GLRenderer.updateShaderSourceData(GLRenderer.java:1658)
                                                                                                    	at com.jme3.renderer.opengl.GLRenderer.updateShaderData(GLRenderer.java:1685)
                                                                                                    	at com.jme3.renderer.opengl.GLRenderer.setShader(GLRenderer.java:1750)

After some more investigation I found that the first part is the problem:

#ifdef GL_ES
  #ifdef FRAGMENT_SHADER
    precision highp float;
    precision highp int;
    precision highp sampler2DArray;
    precision highp sampler2DShadow;
    precision highp samplerCube;
    precision highp sampler3D;
    precision highp sampler2D;
    #if __VERSION__ >= 310
      precision highp sampler2DMS;
    #endif
  #endif
#endif

[stephengold]

Thanks for documenting the issue, @nickidebruyn!

[stephengold]

According to "git blame", the failing code was last modified by PR #2217, which was integrated between v3.7.0-alpha2 and v3.7.0-beta1.

@nickidebruyn Do your Android projects work with JME v3.7.0-alpha2 ?

[nickidebruyn]

I tested a few scenarios for this. I can confirm that none of the new version (v3.7.0-alpha2, v3.7.0-beta1, v3.7.0-stable) works.
I then tested again with v3.6.1 and it worked again.
After that I changed back to v3.7.0-stable and created my own local GLSLCompat.glsllib and changed the frag shader to point to that and it worked again. This is the code I removed from my local: GLSLCompat.glsllib

#ifdef GL_ES
  #ifdef FRAGMENT_SHADER
    precision highp float;
    precision highp int;
    precision highp sampler2DArray;
    precision highp sampler2DShadow;
    precision highp samplerCube;
    precision highp sampler3D;
    precision highp sampler2D;
    #if __VERSION__ >= 310
      precision highp sampler2DMS;
    #endif
  #endif
#endif

[stephengold]

Thank you for the investigation.
Based on your findings, I'm convinced PR #2061 caused the regression.
At the time (August 2023), Riccardo indicated 2061 would need to be tested on Android.
Apparently it never got such testing, and neither did JME 3.7!
I think this calls for a 3.7.1 release...

[nickidebruyn]

Agree, that is probably a good decision.
Most shaders uses that lib.

[pavly-gerges]

What's the status of this issue? Are there any working PRs to fix this?

[yaRnMcDonuts]

I've never looked into the code in GLSLCompat.glsllib and unfortunately I don't have any android experience with jme, so I can't test things to feel certain enough to confidently provide a solution.

But I'd agree with @sgold that this PR likely caused the issue: riccardobl@4e851bf

I'm not particularly knowledgeable when it comes to knowing which exact fragment/vertex shader versions and features to use in each situation especially on android, but it sounds like the "precision highp" is not fully supported on android.

And, from my understanding, this code is simply trying to set the precision for each shader varType which I'm rading mixed things about whether that's even necessary.

But I think some of this info I'm reading is coming from AI, and the rest from random stack overflow posts... so I am skeptical until I can confirm this information from another source, or preferably from our own testing.

Nonetheless, what I'm reading is saying that:

setting precision for types other than float and int (like sampler2DArray, samplerCube, etc.) is unnecessary in most cases.

Only float and int have multiple precision levels in GLSL.

highp, mediump, and lowp only apply to floating-point and integer types.
Example: highp float, mediump int, etc.
Samplers (sampler2D, samplerCube, etc.) are not affected by precision.

Samplers are not numerical types—they are handles to textures.
The precision of texture sampling is controlled by hardware, not by GLSL precision qualifiers.
This means precision highp sampler2D; does nothing.

So, unless I'm mistaken, the only potentially useful code changed in GLSLCompat in that PR is these 2 lines:

precision highp float; precision highp int;

And it sounds like both of these highp int/float precision qualifiers should also be okay on android. And if not, then something like a (#if VERSION >= 300) check around that code should prevent it from running on android devices that don't support highp int or float. But we'll have to try and find out I guess.

So to conclude, (from my limited understanding), the highp precision on non-numerical varTypes is unsupported on android, and it is unnecessary and redundant on desktop since desktop will already default to using highp for everything if supported. But android defaults to mediump or lowp when nothing is set, so I think it is still good to declare int and float as highp if the android version supports it.

Here's what I think is the best solution from my understanding thus far, feedback is greatly appreciated though: #2381

[pavly-gerges]

I tested a few scenarios for this. I can confirm that none of the new version (v3.7.0-alpha2, v3.7.0-beta1, v3.7.0-stable) works.
I then tested again with v3.6.1 and it worked again.
After that I changed back to v3.7.0-stable and created my own local GLSLCompat.glsllib and changed the frag shader to point to that and it worked again. This is the code I removed from my local: GLSLCompat.glsllib

#ifdef GL_ES
  #ifdef FRAGMENT_SHADER
    precision highp float;
    precision highp int;
    precision highp sampler2DArray;
    precision highp sampler2DShadow;
    precision highp samplerCube;
    precision highp sampler3D;
    precision highp sampler2D;
    #if __VERSION__ >= 310
      precision highp sampler2DMS;
    #endif
  #endif
#endif

So far, it seems that the code added recently requires a 'main()' function to be compiled as a GLSL executable. That's why we get this error:

INTERNAL ERROR: no main() function!
ERROR: 1 compilation errors.  No code generated