ShaderBuilder / better handling of strings variables/attributes

Now values which are not mentioned in the style are still added to
the string literals mapping.

Also an error will be thrown if a style references a missing variable.

src/ol/webgl/ShaderBuilder.js

@@ -3,7 +3,7 @@
  * @module ol/webgl/ShaderBuilder
  */
 
-import {expressionToGlsl, ValueTypes} from '../style/expressions.js';
+import {expressionToGlsl, stringToGlsl, ValueTypes} from '../style/expressions.js';
 
 /**
  * @typedef {Object} VaryingDescription
@@ -445,8 +445,14 @@ export function parseLiteralStyle(style) {
   fragContext.variables.forEach(function(varName) {
     builder.addUniform(`float u_${varName}`);
     uniforms[`u_${varName}`] = function() {
-      return style.variables && style.variables[varName] !== undefined ?
+      if (!style.variables || style.variables[varName] === undefined) {
-        style.variables[varName] : 0;
+        throw new Error(`The following variable is missing from the style: ${varName}`);
+      }
+      let value = style.variables[varName];
+      if (typeof value === 'string') {
+        value = parseFloat(stringToGlsl(vertContext, value));
+      }
+      return value !== undefined ? value : -9999999; // to avoid matching with the first string literal
     };
   });
 
@@ -481,7 +487,7 @@ export function parseLiteralStyle(style) {
         callback: function(feature) {
           let value = feature.get(attributeName);
           if (typeof value === 'string') {
-            value = vertContext.stringLiteralsMap[value];
+            value = parseFloat(stringToGlsl(vertContext, value));
           }
           return value !== undefined ? value : -9999999; // to avoid matching with the first string literal
         }

test/spec/ol/webgl/shaderbuilder.test.js

@@ -402,6 +402,56 @@ void main(void) {
       expect(result.attributes).to.eql([]);
       expect(result.uniforms).to.have.property('u_ratio');
     });
+
+    it('correctly adds string variables to the string literals mapping', function() {
+      const result = parseLiteralStyle({
+        variables: {
+          mySize: 'abcdef'
+        },
+        symbol: {
+          symbolType: 'square',
+          size: ['match', ['var', 'mySize'], 'abc', 10, 'def', 20, 30],
+          color: 'red'
+        }
+      });
+
+      expect(result.uniforms['u_mySize']()).to.be.greaterThan(0);
+    });
+
+    it('throws when a variable is requested but not present in the style', function(done) {
+      const result = parseLiteralStyle({
+        variables: {},
+        symbol: {
+          symbolType: 'square',
+          size: ['var', 'mySize'],
+          color: 'red'
+        }
+      });
+
+      try {
+        result.uniforms['u_mySize']();
+      } catch (e) {
+        done();
+      }
+      done(true);
+    });
+
+    it('throws when a variable is requested but the style does not have a variables dict', function(done) {
+      const result = parseLiteralStyle({
+        symbol: {
+          symbolType: 'square',
+          size: ['var', 'mySize'],
+          color: 'red'
+        }
+      });
+
+      try {
+        result.uniforms['u_mySize']();
+      } catch (e) {
+        done();
+      }
+      done(true);
+    });
   });
 
 });