WebGL Varyings Error

[JR Smith]

I am having trouble with a linker error in WebGL that popped up in Chrome. This particular set of shaders all worked in Chrome and Firefox before.  Now it only works in Firefox. 

Error message:

Uncaught Error linking shaders:Varyings with the same name but different type, or statically used varyings in fragment shader are not declared in vertex shader: vColor

Before I post a frag/vert shader, I want to point out that as a test I ran through all of my frag shaders and gave it a static color. The program linked just fine. 

basic.frag

precision mediump float;

precision mediump int;

varying vec4 vColor;

void main(void) {

gl_FragColor = vColor;

}

point.vert

precision mediump float;

precision mediump int;

attribute vec3 aVertexPosition;

attribute vec4 aVertexColor;

uniform mat4 uModelViewMatrix;

uniform mat4 uProjectionMatrix;

uniform float uPointSize;

//for undetermined point attenuation feature

// uniform vec3 uAttenuation;

uniform vec3 uBias;

uniform vec3 uScale;

uniform int uCEMode;

varying vec4 vColor;

void main(void) {

if(uCEMode == 1) {

//use bias and scale unifroms for min max color enhancement

vColor = (aVertexColor - vec4(uBias, 0.0)) * vec4(uScale, 1.0);

}

else {

vColor = aVertexColor;

}

vec4 ecPos4 = uModelViewMatrix * vec4(aVertexPosition, 1.0);

//make points larger as they get further away from the viewer

//helps to make the cloud look less sparse when far enough to only see

//the first level or two of the octree

gl_PointSize = length(ecPos4) / uPointSize * 3.0;

//for undetermined point attenuation feature

// float attn = uAttenuation[0] + (uAttenuation[1] * dist) + (uAttenuation[2] * dist * dist);

// gl_PointSize = (attn > 0.0 && attn < uPointSize) ? uPointSize * sqrt(1.0/attn) : uPointSize;

gl_Position = uProjectionMatrix * ecPos4;

}

I've tried adding lowp/mediump/highp. I've tried declaring it at the top of all the files and individually for each variable. The error message tells me nothing since, as it is hopefully clear above, the varying vColor is the same thing. I've done all the googling I can think of, checked the spec, and even read some tutorials - which also didn't work in Chrome but worked in Firefox.

Last checklist:

- Chrome is updated

- Windows 7 updated

- Chrome's cache is cleared

- Use console watch variables and breakpoints to make sure it's pulling the right shaders

- WebGL is enabled in checking chrome://gpu/

I'm hoping someone can either see what's wrong with the above code or provide something else for me to check (or remind me of something I didn't include in my writeup).

[JR Smith]

I went to webglreport.com after this to pull down all the pertinent info. I hope this helps:

Platform:	Win32
Browser User Agent:	Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.89 Safari/537.36
Context Name:	webgl
GL Version:	WebGL 1.0 (OpenGL ES 2.0 Chromium)
Shading Language Version:	WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor:	WebKit
Renderer:	WebKit WebGL
Unmasked Vendor:	Google Inc.
Unmasked Renderer:	ANGLE (Intel(R) HD Graphics 4000 Direct3D11 vs_5_0 ps_5_0)
Antialiasing:	Available
ANGLE:	Yes, D3D11
Major Performance Caveat:	No
Vertex Shader Max Vertex Attributes: 16 Max Vertex Uniform Vectors: 1024 Max Vertex Texture Image Units: 16 Max Varying Vectors: 28 Best float precision: [-2127, 2127] (23) Transform Feedback Coming in WebGL 2 Rasterizer Aliased Line Width Range: [1, 1] Aliased Point Size Range: [1, 1024] Fragment Shader Max Fragment Uniform Vectors: 1024 Max Texture Image Units: 16 float/int precision: highp/highp Best float precision: [-2127, 2127] (23) Framebuffer Max Color Buffers: 8 RGBA Bits: [8, 8, 8, 8] Depth / Stencil Bits: [24, 8] Max Render Buffer Size: 16384 Max Viewport Dimensions: [16384, 16384] Textures Max Texture Size: 16384 Max Cube Map Texture Size: 16384 Max Combined Texture Image Units: 32 Max Anisotropy: 16 Uniform Buffers Coming in WebGL 2
Supported Extensions:
	ANGLE_instanced_arrays
	EXT_blend_minmax
	EXT_frag_depth
	EXT_shader_texture_lod
	EXT_sRGB
	EXT_texture_filter_anisotropic
	WEBKIT_EXT_texture_filter_anisotropic
	OES_element_index_uint
	OES_standard_derivatives
	OES_texture_float
	OES_texture_float_linear
	OES_texture_half_float
	OES_texture_half_float_linear
	OES_vertex_array_object
	WEBGL_compressed_texture_s3tc
	WEBKIT_WEBGL_compressed_texture_s3tc
	WEBGL_debug_renderer_info
	WEBGL_debug_shaders
	WEBGL_depth_texture
	WEBKIT_WEBGL_depth_texture
	WEBGL_draw_buffers
	WEBGL_lose_context
	WEBKIT_WEBGL_lose_context

 

[Alecazam]

You might try converting uCEMode to a bool.   There are specific static and dynamic branching registers for bools.  If you use an int all bets are off.   int was meant for indexing only (skinning).   

[JR Smith]

Thank you for the suggestion, but that change doesn't change the error mentioned above.

[Alecazam]

My guess is it's a bug in Angle shader translator.  You can try without the branch (just have two shaders), and see if that fixes.   You can always try the GL backend and see if that works, and also download the Angle source to see where it's shader translation is going awry.

[Zhenyao Mo]

OK, I'll debug a little and get back to you soon. Thanks for reporting this.

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[Zhenyao Mo]

So I tested on Linux with top of tree Chromium build with the two shaders, and it compiled and linked fine for me.

So it seems like a win only bug

fragment:

precision mediump float;

precision mediump int;

varying vec4 vColor;

void main(void) {

gl_FragColor = vColor;

}

vertex:

[Geoff Lang]

I tried compiling the shader in chrome M42 and M43 and didn't see any link errors.  It could be an M41-only issue or requires more than just the shader to repro.

[Jamie Madill]

Just a note that I tried in ANGLE D3D11 on Chrome M41 and didn't repro the bug. If you can find a repro case, please open a bug on crbug.com with the contents of your about:gpu. Also trying in Canary wouldn't hurt.

[Kenneth Russell]

I wonder whether the problem might be a bug in Chrome's shader cache. There have been a couple of bugs discovered and fixed recently, usually involving compiling shaders and linking programs multiple times.

Try running Chrome from the command line with the argument --user-data-dir=[temporary directory]. If that clears up the problem then there's likely a bug in the shader cache. It would be great if you could try to figure out reproduction steps in that case.