WebGLRenderer: added clamping of user specified precision to maximum available.

For the moment just continuing with having both vertex and fragment shaders using the same precision (not to get uniforms precision mismatch, see #1602).

See #2769

src/renderers/WebGLRenderer.js

@@ -198,6 +198,52 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	var _compressedTextureFormats = _glExtensionCompressedTextureS3TC ? _gl.getParameter( _gl.COMPRESSED_TEXTURE_FORMATS ) : [];
 
+	//
+
+	var _vertexShaderPrecisionHighpFloat = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.HIGH_FLOAT );
+	var _vertexShaderPrecisionMediumpFloat = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.MEDIUM_FLOAT );
+	var _vertexShaderPrecisionLowpFloat = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.LOW_FLOAT );
+
+	var _fragmentShaderPrecisionHighpFloat = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.HIGH_FLOAT );
+	var _fragmentShaderPrecisionMediumpFloat = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.MEDIUM_FLOAT );
+	var _fragmentShaderPrecisionLowpFloat = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.LOW_FLOAT );
+
+	var _vertexShaderPrecisionHighpInt = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.HIGH_INT );
+	var _vertexShaderPrecisionMediumpInt = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.MEDIUM_INT );
+	var _vertexShaderPrecisionLowpInt = _gl.getShaderPrecisionFormat( _gl.VERTEX_SHADER, _gl.LOW_INT );
+
+	var _fragmentShaderPrecisionHighpInt = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.HIGH_INT );
+	var _fragmentShaderPrecisionMediumpInt = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.MEDIUM_INT );
+	var _fragmentShaderPrecisionLowpInt = _gl.getShaderPrecisionFormat( _gl.FRAGMENT_SHADER, _gl.LOW_INT );
+
+	// clamp precision to maximum available
+
+	var highpAvailable = _vertexShaderPrecisionHighpFloat.precision > 0 && _fragmentShaderPrecisionHighpFloat.precision > 0;
+	var mediumpAvailable = _vertexShaderPrecisionMediumpFloat.precision > 0 && _fragmentShaderPrecisionMediumpFloat.precision > 0;
+
+	if ( _precision === "highp" && ! highpAvailable ) {
+
+		if ( mediumpAvailable ) {
+
+			_precision = "mediump";
+			console.warn( "WebGLRenderer: highp not supported, using mediump" );
+
+		} else {
+
+			_precision = "lowp";
+			console.warn( "WebGLRenderer: highp and mediump not supported, using lowp" );
+
+		}
+
+	}
+
+	if ( _precision === "mediump" && ! mediumpAvailable ) {
+
+		_precision = "lowp";
+		console.warn( "WebGLRenderer: mediump not supported, using lowp" );
+
+	}
+
 	// API
 
 	this.getContext = function () {
@@ -5458,7 +5504,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 		if ( textureUnit >= _maxTextures ) {
 
-			console.warn( "Trying to use " + textureUnit + " texture units while this GPU supports only " + _maxTextures );
+			console.warn( "WebGLRenderer: trying to use " + textureUnit + " texture units while this GPU supports only " + _maxTextures );
 
 		}