[Samples] New DrawingArea sample

Source/Samples/Sections/Widgets/DrawingAreaSection.cs

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+// This is free and unencumbered software released into the public domain.
+// Happy coding!!! - GtkSharp Team
+
+// Ported from https://developer.gnome.org/gtkmm-tutorial/3.24/gtkmm-tutorial.html
+
+using Cairo;
+using Gtk;
+using System;
+
+namespace Samples
+{
+    [Section(ContentType = typeof(DrawingArea), Category = Category.Widgets)]
+    class DrawingAreaSection : ListSection
+    {
+        public DrawingAreaSection()
+        {
+            AddItem(DrawCircles());
+            AddItem(DrawText());
+        }
+
+        public (string, Widget) DrawCircles()
+        {
+            DrawingArea drawingArea = new DrawingArea();
+            drawingArea.SetSizeRequest(50,50);
+            drawingArea.Drawn += DrawingAreaCirclesOnDrawn;
+
+            return ("Draw Circles :", drawingArea);
+        }
+
+        public (string, Widget) DrawText()
+        {
+            DrawingArea drawingArea = new DrawingArea();
+            drawingArea.SetSizeRequest(200,100);
+            drawingArea.Drawn += DrawingAreaTextOnDrawn;
+
+            return ("Draw Pango Text :", drawingArea);
+        }
+        
+        private void DrawingAreaCirclesOnDrawn(object o, DrawnArgs args)
+        {
+            if (o is DrawingArea da)
+            {
+                Context cr = args.Cr;
+                
+                int width = da.Allocation.Width;
+                int height = da.Allocation.Height;
+                
+                cr.LineWidth = 5;
+                cr.SetSourceRGB(0.8, 0.8, 0.8);
+                
+                cr.Rectangle(0, 0, width, height);
+                cr.Fill();
+                
+                cr.SetSourceRGB(0.9, 0, 0);
+                cr.Translate(width/2d, height/2d);
+                cr.Arc(0, 0, (width < height ? width : height) / 2 - 10, 0, 2*Math.PI);
+                cr.StrokePreserve();
+                
+                cr.SetSourceRGB(0, 0.9, 0);
+                cr.Fill();
+                
+                cr.GetTarget().Dispose();
+                cr.Dispose();
+            } 
+        }
+                
+        private void DrawingAreaTextOnDrawn(object o, DrawnArgs args)
+        {
+            if (o is DrawingArea da)
+            {
+                Context cr = args.Cr;
+
+                int width = da.Allocation.Width;
+                int height = da.Allocation.Height;
+                
+                int rectangle_width = width;
+                int rectangle_height = height / 2;
+                
+                // Draw a black rectangle
+                cr.SetSourceRGB(0, 0, 0);
+                cr.Rectangle(0, 0, rectangle_width, rectangle_height);
+                cr.Fill();
+                
+                // and some white text
+                cr.SetSourceRGB(1.0, 1.0, 1.0);
+                draw_text(cr, rectangle_width, rectangle_height, "Hi there!");
+                
+                // flip the image vertically
+                // see http://www.cairographics.org/documentation/cairomm/reference/classCairo_1_1Matrix.html
+                // the -1 corresponds to the yy part (the flipping part)
+                // the height part is a translation (we could have just called cr->translate(0, height) instead)
+                // it's height and not height / 2, since we want this to be on the second part of our drawing
+                // (otherwise, it would draw over the previous part)
+                Cairo.Matrix matrix = new Matrix(1.0, 0.0, 0.0, -1.0, 0.0, height);
+                
+                // apply the matrix
+                cr.Transform(matrix);
+                
+                // white rectangle
+                cr.SetSourceRGB(1.0, 1.0, 1.0);
+                cr.Rectangle(0, 0, rectangle_width, rectangle_height);
+                cr.Fill();
+
+                // black text
+                cr.SetSourceRGB(0, 0, 0);
+                draw_text(cr, rectangle_width, rectangle_height, "Hi there!");
+                
+                cr.GetTarget().Dispose();
+                cr.Dispose();
+            } 
+        }
+        
+        private void draw_text(Context cr, int rectangle_width, int rectangle_height, string text)
+        {
+            // http://developer.gnome.org/pangomm/unstable/classPango_1_1FontDescription.html
+            Pango.FontDescription font = new Pango.FontDescription();
+
+            font.Family = "Monospace";
+            font.Weight = Pango.Weight.Bold;
+
+            // http://developer.gnome.org/pangomm/unstable/classPango_1_1Layout.html
+            Pango.Layout layout = CreatePangoLayout(text);
+
+            layout.FontDescription = font;
+
+            int text_width;
+            int text_height;
+
+            //get the text dimensions (it updates the variables -- by reference)
+            layout.GetPixelSize(out text_width, out text_height);
+
+            // Position the text in the middle
+            cr.MoveTo((rectangle_width - text_width) / 2d, (rectangle_height - text_height) / 2d);
+
+            Pango.CairoHelper.ShowLayout(cr, layout);
+        }
+    }
+}