message: fix glsl300 frag shader prefix
diff: @@ -201,13 +201,17 @@ const glsl300FragPrefixCommon = `
  #define gl_FragColor out_FragData0
  #define gl_FragDepthEXT gl_FragDepth
  -#define enabledStandardDerivatives
  -#define enabledFragDepth
  #define requiredDrawBuffers
  `
  function getGlsl300FragPrefix(gl: WebGL2RenderingContext, extensions: WebGLExtensions, shaderExtensions: ShaderExtensions) {
  const prefix = [ '#version 300 es' ]
  + if (shaderExtensions.standardDerivatives) {
  + prefix.push('#define enabledStandardDerivatives')
  + }
  + if (shaderExtensions.fragDepth) {
  + prefix.push('#define enabledFragDepth')
  + }
  if (extensions.drawBuffers) {
  const maxDrawBuffers = gl.getParameter(gl.MAX_DRAW_BUFFERS) as number
  for (let i = 0, il = maxDrawBuffers; i < il; ++i) {
  