#5740: Better implementation of IFace::getTexelScale(). Add unit test…

… checking the pivoted rotation preserving texel scale

radiantcore/brush/Face.cpp

@@ -521,7 +521,13 @@ Vector2 Face::getTexelScale() const
     auto imageHeight = _shader.getHeight();
 
     auto textureMatrix = _texdef.getMatrix();
-    return Vector2(textureMatrix.xx() * imageWidth, textureMatrix.yy() * imageHeight);
+
+    // Multiplying the image dimensions onto the texture matrix yields
+    // the base vectors in texel space. Take the length to get the covered texels per world unit
+    return Vector2(
+        Vector2(textureMatrix.xx() * imageWidth, textureMatrix.xy() * imageHeight).getLength(),
+        Vector2(textureMatrix.yx() * imageWidth, textureMatrix.yy() * imageHeight).getLength()
+    );
 }
 
 float Face::getTextureAspectRatio() const

test/TextureManipulation.cpp

@@ -698,4 +698,24 @@ TEST_F(TextureManipulationTest, FaceTextureChangePreservesTexelScale)
     EXPECT_NEAR(texelScaleBefore.y(), texelScaleAfter.y(), 0.01) << "Texel scale Y changed after applying new material";
 }
 
+TEST_F(TextureManipulationTest, FaceRotationPreservesTexelScale)
+{
+    auto material = "textures/a_1024x512";
+    auto worldspawn = GlobalMapModule().findOrInsertWorldspawn();
+    auto test1024x512Node = algorithm::createCuboidBrush(worldspawn, AABB({ 128, 32, 16 }, { 128, 32, 16 }), material);
+    algorithm::foreachFace(*Node_getIBrush(test1024x512Node), [](IFace& face) { face.fitTexture(1, 1); });
+
+    auto& face = *algorithm::findBrushFaceWithNormal(Node_getIBrush(test1024x512Node), { 0, 0, 1 });
+
+    auto texelScaleBefore = face.getTexelScale();
+
+    face.rotateTexdef(45); // degrees
+    face.rotateTexdef(45);
+
+    auto texelScaleAfter = face.getTexelScale();
+
+    EXPECT_NEAR(texelScaleBefore.x(), texelScaleAfter.x(), 0.01) << "Texel scale X changed after rotation by 90 degrees";
+    EXPECT_NEAR(texelScaleBefore.y(), texelScaleAfter.y(), 0.01) << "Texel scale Y changed after rotation by 90 degrees";
+}
+
 }