"Failed to compile fragment shader: 0:2(1): error: No precision specified in this scope for type `vec2'" with Flutter 3.22

[Saviq]

Steps to reproduce

Run a Flutter app on a Raspberry Pi arm64.

Expected results

Rendered app.

Actual results

The app is black and this is logged:

WARNING **: 13:47:43.682: Failed to compile fragment shader: 0:2(1): error: No precision specified in this scope for type `vec2'
WARNING **: 13:47:43.683: Failed to link program: error: linking with uncompiled/unspecialized shader

Code sample

Just the hello_world app

[hlvs-apps]

Also occurs on x64 ubuntu 22 / ubuntu core with snap packaging of the flutter app

[Saviq]

@hlvs-apps FYI here's a workaround I've applied to one of our snaps:

canonical/ubuntu-frame@e149fa7

Using flutter-channel: master would work, too - as that's not using the shader path any more.

[KadirovKmck]

Steps to Reproduce

1. Set up your development environment:

   • Ensure you have a Raspberry Pi with an ARM64 architecture.
   • Install the necessary dependencies for Flutter on your Raspberry Pi.

2. Install Flutter:

   • Follow the official Flutter installation guide to set up Flutter on your Raspberry Pi.

3. Create a simple Flutter app:

   • Use the Flutter command to create a new Flutter project:

     flutter create hello_world

4. Run the Flutter app:

   • Navigate to the newly created project directory:

     cd hello_world

   • Run the Flutter app on your Raspberry Pi:

     flutter run

Expected Results

• The Flutter app should render correctly, displaying the "Hello, World!" message.

Actual Results

• The app screen is black, and the following warning is logged:

  WARNING **: 13:47:43.682: Failed to compile fragment shader: 0:2(1): error: No precision specified in this scope for type `vec2'
  WARNING **: 13:47:43.683: Failed to link program: error: linking with uncompiled/unspecialized shader
  

Analysis and Solution

The warnings indicate that there is an issue with the shader compilation on the Raspberry Pi, specifically related to the precision qualifiers in GLSL (OpenGL Shading Language).

Solution Steps

1. Modify Shader Code:

   • Ensure that the fragment shaders include precision qualifiers for the vec2 type.
   • Locate the shader code within your Flutter project or Flutter engine source. This might be in the flutter/engine repository if you're building from source.

2. Patch the Shader Code:

   • Add the appropriate precision qualifier to the fragment shader code. For instance:

     precision mediump float;

   • Example of how to modify a fragment shader:

     #version 300 es
     precision mediump float;
     layout(location = 0) out vec4 fragColor;
     
     in vec2 v_texCoord;
     
     uniform sampler2D u_texture;
     
     void main() {
       fragColor = texture(u_texture, v_texCoord);
     }

3. Rebuild the Flutter Engine:

   • If you modified the shader code in the Flutter engine, you will need to rebuild the Flutter engine for ARM64.
   • Follow the official Flutter guide to build the engine from source for ARM64.

4. Deploy the Updated Engine:

   • Replace the existing Flutter engine on your Raspberry Pi with the newly built engine that includes the shader fixes.

5. Run the App Again:

   • Retry running your Flutter app to ensure the shader compilation issue is resolved.

Example Code

Here's a hypothetical example demonstrating how to specify the precision qualifier in a fragment shader. Ensure your shaders follow a similar pattern:

// Example fragment shader with precision qualifier
#version 300 es
precision mediump float;

in vec2 v_texCoord;
out vec4 fragColor;

uniform sampler2D u_texture;

void main() {
  fragColor = texture(u_texture, v_texCoord);
}

Conclusion

By adding the precision qualifiers to your GLSL fragment shaders and rebuilding the Flutter engine, you can resolve the shader compilation errors and successfully run Flutter apps on a Raspberry Pi ARM64. Ensure you thoroughly test the modified shaders on your target hardware to confirm the fix.

[krille-chan]

Also occurs with Flutter 3.24.0, blocking me from updating to the next flutter version since months...

[CharleeSF]

So it works on master and not on flutter 3.24?