Expressions / rework the interpolate operator

This operator is now able to map numbers to output ranges as well as colors,
making the stretch operator unnecessary. Also allows giving multiple stops,
like in Mapbox style spec.

test/spec/ol/style/expressions.test.js

@@ -169,8 +169,6 @@ describe('ol.style.expressions', function() {
       expect(expressionToGlsl(context, ['==', 10, ['get', 'attr4']])).to.eql('(10.0 == a_attr4)');
       expect(expressionToGlsl(context, ['between', ['get', 'attr4'], -4.0, 5.0])).to.eql('(a_attr4 >= -4.0 && a_attr4 <= 5.0)');
       expect(expressionToGlsl(context, ['!', ['get', 'attr4']])).to.eql('(!a_attr4)');
-      expect(expressionToGlsl(context, ['interpolate', ['get', 'attr4'], [255, 255, 255, 1], 'transparent'])).to.eql(
-        'mix(vec4(1.0, 1.0, 1.0, 1.0), vec4(0.0, 0.0, 0.0, 0.0), a_attr4)');
     });
 
     it('correctly adapts output for fragment shaders', function() {
@@ -211,11 +209,6 @@ describe('ol.style.expressions', function() {
       } catch (e) {
         thrown = true;
       }
-      try {
-        expressionToGlsl(context, ['interpolate', ['get', 'attr4'], 1, '#3344FF']);
-      } catch (e) {
-        thrown = true;
-      }
       expect(thrown).to.be(true);
     });
 
@@ -331,6 +324,13 @@ describe('ol.style.expressions', function() {
         thrown = true;
       }
       expect(thrown).to.be(true);
+
+      try {
+        expressionToGlsl(context, ['match', ['get', 'attr'], 0]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
     });
 
     it('correctly parses the expression (colors)', function() {
@@ -358,6 +358,122 @@ describe('ol.style.expressions', function() {
 
   });
 
+  describe('interpolate operator', function() {
+    let context;
+
+    beforeEach(function() {
+      context = {
+        variables: [],
+        attributes: [],
+        stringLiteralsMap: {}
+      };
+    });
+
+    it('correctly guesses the output type', function() {
+      expect(getValueType(['interpolate', ['linear'], ['get', 'attr'], 0, 'red', 100, 'yellow']))
+        .to.eql(ValueTypes.COLOR);
+      expect(getValueType(['interpolate', ['linear'], ['get', 'attr'], 0, [1, 2, 3], 1, [0, 0, 0, 4]]))
+        .to.eql(ValueTypes.COLOR);
+      expect(getValueType(['interpolate', ['linear'], ['get', 'attr'], 1000, -10, 2000, 10]))
+        .to.eql(ValueTypes.NUMBER);
+    });
+
+    it('throws if no single output type could be inferred', function() {
+      let thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['linear'], ['get', 'attr'], 1000, -10, 2000, 10], ValueTypes.COLOR);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+
+      try {
+        expressionToGlsl(context, ['interpolate', ['linear'], ['get', 'attr'], 0, [1, 2, 3], 1, 222]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+
+      thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['linear'], ['get', 'attr'], 0, [1, 2, 3], 1, [0, 0, 0, 4]], ValueTypes.NUMBER);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+    });
+
+    it('throws if invalid argument count', function() {
+      let thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['linear'], ['get', 'attr'], 1000]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+
+      thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['linear'], ['get', 'attr'], 1000, -10, 2000, 10, 5000]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+    });
+
+    it('throws if an invalid interpolation type is given', function() {
+      let thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', 'linear', ['get', 'attr'], 1000, 0, 2000, 1]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+
+      thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['exponential'], ['get', 'attr'], 1000, -10, 2000, 1]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+
+      thrown = false;
+      try {
+        expressionToGlsl(context, ['interpolate', ['not_a_type'], ['get', 'attr'], 1000, -10, 2000, 1]);
+      } catch (e) {
+        thrown = true;
+      }
+      expect(thrown).to.be(true);
+    });
+
+    it('correctly parses the expression (colors, linear)', function() {
+      expect(expressionToGlsl(context,
+        ['interpolate', ['linear'], ['get', 'attr'], 1000, [255, 0, 0], 2000, [0, 255, 0]]
+      )).to.eql(
+        'mix(vec4(1.0, 0.0, 0.0, 1.0), vec4(0.0, 1.0, 0.0, 1.0), pow(clamp((a_attr - 1000.0) / (2000.0 - 1000.0), 0.0, 1.0), 1.0))');
+      expect(expressionToGlsl(context,
+        ['interpolate', ['linear'], ['get', 'attr'], 1000, [255, 0, 0], 2000, [0, 255, 0], 5000, [0, 0, 255]]
+      )).to.eql(
+        'mix(mix(vec4(1.0, 0.0, 0.0, 1.0), vec4(0.0, 1.0, 0.0, 1.0), pow(clamp((a_attr - 1000.0) / (2000.0 - 1000.0), 0.0, 1.0), 1.0)), vec4(0.0, 0.0, 1.0, 1.0), pow(clamp((a_attr - 2000.0) / (5000.0 - 2000.0), 0.0, 1.0), 1.0))');
+    });
+
+    it('correctly parses the expression (number, linear)', function() {
+      expect(expressionToGlsl(context,
+        ['interpolate', ['linear'], ['get', 'attr'], 1000, -10, 2000, 0, 5000, 10]
+      )).to.eql(
+        'mix(mix(-10.0, 0.0, pow(clamp((a_attr - 1000.0) / (2000.0 - 1000.0), 0.0, 1.0), 1.0)), 10.0, pow(clamp((a_attr - 2000.0) / (5000.0 - 2000.0), 0.0, 1.0), 1.0))');
+    });
+
+    it('correctly parses the expression (number, exponential)', function() {
+      expect(expressionToGlsl(context,
+        ['interpolate', ['exponential', 0.5], ['get', 'attr'], 1000, -10, 2000, 0, 5000, 10]
+      )).to.eql(
+        'mix(mix(-10.0, 0.0, pow(clamp((a_attr - 1000.0) / (2000.0 - 1000.0), 0.0, 1.0), 0.5)), 10.0, pow(clamp((a_attr - 2000.0) / (5000.0 - 2000.0), 0.0, 1.0), 0.5))');
+    });
+
+  });
+
   describe('complex expressions', function() {
     let context;