GraphicsDemo: Add new demo showing blur and transparency effects

examples/GUI/GraphicsDemo.h

@@ -516,6 +516,82 @@ public:
     std::unique_ptr<Drawable> svgDrawable;
 };
 
+class BlurDemo final : public GraphicsDemoBase
+{
+public:
+    BlurDemo (ControllersComponent& cc)
+        : GraphicsDemoBase (cc, "Blur")
+    {
+        image.setBackupEnabled (false);
+    }
+
+    void drawDemo (Graphics& g) override
+    {
+        const auto a = lopassA.next (jmap (frequencyA.getValue(), 0.09f, 0.12f));
+        const auto b = lopassB.next (jmap (frequencyB.getValue(), 0.09f, 0.12f));
+
+        initialPhase += 0.01f;
+        initialPhase -= (float) (int) initialPhase;
+        const auto startAngle = initialPhase * MathConstants<float>::twoPi;
+        const auto centreSquare = image.getBounds().reduced (100);
+
+        {
+            Graphics g2 { image };
+            g2.setColour (Colours::transparentBlack);
+            g2.excludeClipRegion (centreSquare);
+            g2.getInternalContext().fillRect (image.getBounds(), true);
+        }
+
+        if (auto ptr = image.getClippedImage (centreSquare).getPixelData())
+        {
+            ptr->applyGaussianBlurEffect (7.0f);
+            ptr->multiplyAllAlphas (0.98f);
+        }
+
+        {
+            Graphics g2 { image };
+            const auto baseColour = Colours::cyan;
+            const auto destColour = Colours::magenta;
+            const auto offset = image.getBounds().getCentre().toFloat();
+            const auto numSegments = 200;
+
+            for (auto i = 0; i < numSegments; ++i)
+            {
+                g2.setColour (baseColour.interpolatedWith (destColour, (float) i / numSegments));
+
+                const auto getPoint = [&] (auto ind)
+                {
+                    return offset + Point { 200 * std::sin (startAngle + a * (float) ind),
+                                            200 * std::cos (startAngle + b * (float) ind) };
+                };
+
+                g2.drawLine ({ getPoint (i), getPoint (i + 1) }, 2.0f);
+            }
+        }
+
+        AffineTransform transform (AffineTransform::translation ((float) (-image.getWidth()  / 2),
+                                                                 (float) (-image.getHeight() / 2))
+                                   .followedBy (getTransform()));
+
+        g.setOpacity (getAlpha());
+        g.drawImageTransformed (image, transform, false);
+    }
+
+    class Lopass
+    {
+    public:
+        float next (float f) { return value += (f - value) * 0.05f; }
+
+    private:
+        float value{};
+    };
+
+    Image image { Image::ARGB, 512, 512, true };
+    SlowerBouncingNumber frequencyA, frequencyB;
+    Lopass lopassA, lopassB;
+    float initialPhase = 0.0f;
+};
+
 //==============================================================================
 class LinesDemo final : public GraphicsDemoBase
 {
@@ -687,6 +763,7 @@ public:
         demos.add (new ImagesRenderingDemo (controls, false, true));
         demos.add (new ImagesRenderingDemo (controls, true,  false));
         demos.add (new ImagesRenderingDemo (controls, true,  true));
+        demos.add (new BlurDemo   (controls));
         demos.add (new GlyphsDemo (controls));
         demos.add (new SVGDemo    (controls));
         demos.add (new LinesDemo  (controls));