shader method Null safety

Shader shader(
  1. {Float32List? floatUniforms,
  2. List<ImageShader>? samplerUniforms}
)

Constructs a Shader object suitable for use by Paint.shader with the given uniforms.

This method is suitable to be called synchronously within a widget's build method or from CustomPainter.paint.

floatUniforms can be passed optionally to initialize the shader's uniforms. If they are not set they will each default to 0.

When initializing floatUniforms, the length of float uniforms must match the total number of floats defined as uniforms in the shader, or an ArgumentError will be thrown. Details are below.

Consider the following snippit of GLSL code.

layout (location = 0) uniform float a;
layout (location = 1) uniform vec2 b;
layout (location = 2) uniform vec3 c;
layout (location = 3) uniform mat2x2 d;

When compiled to SPIR-V and provided to the constructor, floatUniforms must have a length of 10. One per float-component of each uniform.

program.shader(floatUniforms: Float32List.fromList([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]));

The uniforms will be set as follows:

a: 1 b: 2, 3 c: 4, 5, 6 d: 7, 8, 9, 10 // 2x2 matrix in column-major order

imageSamplers must also be sized correctly, matching the number of UniformConstant variables of type SampledImage specified in the SPIR-V code.

Consider the following snippit of GLSL code.

layout (location = 0) uniform sampler2D a;
layout (location = 1) uniform sampler2D b;

After being compiled to SPIR-V imageSamplers must have a length of 2.

Once a Shader is built, uniform values cannot be changed. Instead, shader must be called again with new uniform values.

Implementation

Shader shader({
  Float32List? floatUniforms,
  List<ImageShader>? samplerUniforms,
}) {
  if (floatUniforms == null) {
    floatUniforms = Float32List(_uniformFloatCount);
  }
  if (floatUniforms.length != _uniformFloatCount) {
    throw ArgumentError(
      'floatUniforms size: ${floatUniforms.length} must match given shader uniform count: $_uniformFloatCount.');
  }
  if (_samplerCount > 0 && (samplerUniforms == null || samplerUniforms.length != _samplerCount)) {
    throw ArgumentError('samplerUniforms must have length $_samplerCount');
  }
  if (samplerUniforms == null) {
    samplerUniforms = <ImageShader>[];
  } else {
    samplerUniforms = <ImageShader>[...samplerUniforms];
  }
  final _FragmentShader shader = _FragmentShader(
      this, Float32List.fromList(floatUniforms), samplerUniforms);
  _shader(shader, floatUniforms, samplerUniforms);
  return shader;
}