String vertexShaderSource

Source 

@override
String get vertexShaderSource => """

  uniform mat4 uProjectionMatrix;
  attribute vec2 aVertexPosition;
  attribute vec2 aVertexTextCoord;
  attribute float aVertexAlpha;
  varying vec2 vTextCoord;
  varying float vAlpha;

  void main() {
    vTextCoord = aVertexTextCoord;
    vAlpha = aVertexAlpha;
    gl_Position = vec4(aVertexPosition, 0.0, 1.0) * uProjectionMatrix;
  }
  """;