[gtk+/wip/carlosg/stylus-gesture: 2/2] demos: Add "Paint" demo

[Carlos Garnacho <carlosg src gnome org>]

commit 721e3258020bff31ab01a231f80bf5e2e6309979
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Feb 2 16:04:17 2018 +0100

    demos: Add "Paint" demo

 demos/gtk-demo/demo.gresource.xml |    1 +
 demos/gtk-demo/meson.build        |    1 +
 demos/gtk-demo/paint.c            |  273 +++++++++++++++++++++++++++++++++++++
 3 files changed, 275 insertions(+), 0 deletions(-)
---
diff --git a/demos/gtk-demo/demo.gresource.xml b/demos/gtk-demo/demo.gresource.xml
index 2d69cda..42c0705 100644
--- a/demos/gtk-demo/demo.gresource.xml
+++ b/demos/gtk-demo/demo.gresource.xml
@@ -180,6 +180,7 @@
     <file>modelbutton.c</file>
     <file>overlay.c</file>
     <file>overlay2.c</file>
+    <file>paint.c</file>
     <file>pagesetup.c</file>
     <file>panes.c</file>
     <file>pickers.c</file>
diff --git a/demos/gtk-demo/meson.build b/demos/gtk-demo/meson.build
index ed2e58c..ae1bf7e 100644
--- a/demos/gtk-demo/meson.build
+++ b/demos/gtk-demo/meson.build
@@ -45,6 +45,7 @@ demos = files([
   'modelbutton.c',
   'overlay.c',
   'overlay2.c',
+  'paint.c',
   'panes.c',
   'pickers.c',
   'pixbufs.c',
diff --git a/demos/gtk-demo/paint.c b/demos/gtk-demo/paint.c
new file mode 100644
index 0000000..d83c425
--- /dev/null
+++ b/demos/gtk-demo/paint.c
@@ -0,0 +1,273 @@
+/* Paint
+ *
+ * Demonstrates practical handling of drawing tablets in a real world
+ * usecase.
+ */
+#include <gtk/gtk.h>
+
+typedef struct
+{
+  GtkWidget parent_instance;
+  cairo_surface_t *surface;
+  cairo_t *cr;
+  GdkRGBA draw_color;
+
+  GtkGesture *stylus_gesture;
+} DrawingArea;
+
+typedef struct
+{
+  GtkWidgetClass parent_class;
+} DrawingAreaClass;
+
+G_DEFINE_TYPE (DrawingArea, drawing_area, GTK_TYPE_WIDGET)
+
+static void
+drawing_area_ensure_surface (DrawingArea *area,
+                             gint         width,
+                             gint         height)
+{
+  if (!area->surface ||
+      cairo_image_surface_get_width (area->surface) != width ||
+      cairo_image_surface_get_height (area->surface) != height)
+    {
+      cairo_surface_t *surface;
+
+      surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+                                            width, height);
+      if (area->surface)
+        {
+          cairo_t *cr;
+
+          cr = cairo_create (surface);
+          cairo_set_source_surface (cr, area->surface, 0, 0);
+          cairo_paint (cr);
+
+          cairo_surface_destroy (area->surface);
+          cairo_destroy (area->cr);
+          cairo_destroy (cr);
+        }
+
+      area->surface = surface;
+      area->cr = cairo_create (surface);
+    }
+}
+
+static void
+drawing_area_size_allocate (GtkWidget           *widget,
+                            const GtkAllocation *allocation,
+                            int                  baseline,
+                            GtkAllocation       *out_clip)
+{
+  DrawingArea *area = (DrawingArea *) widget;
+
+  drawing_area_ensure_surface (area, allocation->width, allocation->height);
+
+  GTK_WIDGET_CLASS (drawing_area_parent_class)->size_allocate (widget, allocation, baseline, out_clip);
+}
+
+static void
+drawing_area_map (GtkWidget *widget)
+{
+  GtkAllocation allocation;
+
+  GTK_WIDGET_CLASS (drawing_area_parent_class)->map (widget);
+
+  gtk_widget_get_allocation (widget, &allocation);
+  drawing_area_ensure_surface ((DrawingArea *) widget,
+                               allocation.width, allocation.height);
+}
+
+static void
+drawing_area_unmap (GtkWidget *widget)
+{
+  DrawingArea *area = (DrawingArea *) widget;
+
+  g_clear_pointer (&area->cr, cairo_destroy);
+  g_clear_pointer (&area->surface, cairo_surface_destroy);
+
+  GTK_WIDGET_CLASS (drawing_area_parent_class)->unmap (widget);
+}
+
+static gboolean
+drawing_area_draw (GtkWidget *widget,
+                   cairo_t   *cr)
+{
+  DrawingArea *area = (DrawingArea *) widget;
+  GtkAllocation allocation;
+
+  gtk_widget_get_allocation (widget, &allocation);
+  cairo_set_source_rgb (cr, 1, 1, 1);
+  cairo_paint (cr);
+
+  cairo_set_source_surface (cr, area->surface, 0, 0);
+  cairo_paint (cr);
+
+  cairo_set_source_rgb (cr, 0.6, 0.6, 0.6);
+  cairo_rectangle (cr, 0, 0, allocation.width, allocation.height);
+  cairo_stroke (cr);
+
+  return FALSE;
+}
+
+static void
+drawing_area_class_init (DrawingAreaClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  widget_class->size_allocate = drawing_area_size_allocate;
+  widget_class->draw = drawing_area_draw;
+  widget_class->map = drawing_area_map;
+  widget_class->unmap = drawing_area_unmap;
+}
+
+static void
+drawing_area_apply_stroke (DrawingArea   *area,
+                           GdkDeviceTool *tool,
+                           gdouble        x,
+                           gdouble        y,
+                           gdouble        pressure)
+{
+  if (gdk_device_tool_get_tool_type (tool) == GDK_DEVICE_TOOL_TYPE_ERASER)
+    {
+      cairo_set_line_width (area->cr, 10 * pressure);
+      cairo_set_operator (area->cr, CAIRO_OPERATOR_DEST_OUT);
+    }
+  else
+    {
+      cairo_set_line_width (area->cr, 4 * pressure);
+      cairo_set_operator (area->cr, CAIRO_OPERATOR_SATURATE);
+    }
+
+  cairo_set_source_rgba (area->cr, area->draw_color.red,
+                         area->draw_color.green, area->draw_color.blue,
+                         area->draw_color.alpha * pressure);
+
+  //cairo_set_source_rgba (area->cr, 0, 0, 0, pressure);
+
+  cairo_line_to (area->cr, x, y);
+  cairo_stroke (area->cr);
+  cairo_move_to (area->cr, x, y);
+}
+
+static void
+stylus_gesture_down (GtkGestureStylus *gesture,
+                     gdouble           x,
+                     gdouble           y,
+                     DrawingArea      *area)
+{
+  cairo_new_path (area->cr);
+}
+
+static void
+stylus_gesture_motion (GtkGestureStylus *gesture,
+                       gdouble           x,
+                       gdouble           y,
+                       DrawingArea      *area)
+{
+  GdkTimeCoord *backlog;
+  GdkDeviceTool *tool;
+  gdouble pressure;
+  guint n_items;
+
+  tool = gtk_gesture_stylus_get_device_tool (gesture);
+
+  if (gtk_gesture_stylus_get_backlog (gesture, &backlog, &n_items))
+    {
+      guint i;
+
+      for (i = 0; i < n_items; i++)
+        {
+          drawing_area_apply_stroke (area, tool,
+                                     backlog[i].axes[GDK_AXIS_X],
+                                     backlog[i].axes[GDK_AXIS_Y],
+                                     backlog[i].axes[GDK_AXIS_PRESSURE]);
+        }
+    }
+  else
+    {
+      if (!gtk_gesture_stylus_get_axis (gesture, GDK_AXIS_PRESSURE, &pressure))
+        pressure = 1;
+
+      drawing_area_apply_stroke (area, tool, x, y, pressure);
+    }
+
+  gtk_widget_queue_draw (GTK_WIDGET (area));
+}
+
+static void
+drawing_area_init (DrawingArea *area)
+{
+  gtk_widget_set_has_window (GTK_WIDGET (area), FALSE);
+
+  area->stylus_gesture = gtk_gesture_stylus_new (GTK_WIDGET (area));
+  g_signal_connect (area->stylus_gesture, "down",
+                    G_CALLBACK (stylus_gesture_down), area);
+  g_signal_connect (area->stylus_gesture, "motion",
+                    G_CALLBACK (stylus_gesture_motion), area);
+
+  area->draw_color = (GdkRGBA) { 0, 0, 0, 1 };
+}
+
+GtkWidget *
+drawing_area_new (void)
+{
+  return g_object_new (drawing_area_get_type (), NULL);
+}
+
+void
+drawing_area_set_color (DrawingArea *area,
+                        GdkRGBA     *color)
+{
+  area->draw_color = *color;
+}
+
+static void
+color_button_color_set (GtkColorButton *button,
+                        DrawingArea    *draw_area)
+{
+  GdkRGBA color;
+
+  gtk_color_chooser_get_rgba (GTK_COLOR_CHOOSER (button), &color);
+  drawing_area_set_color (draw_area, &color);
+}
+
+GtkWidget *
+do_paint (GtkWidget *toplevel)
+{
+  static GtkWidget *window = NULL;
+
+  if (!window)
+    {
+      GtkWidget *draw_area, *headerbar, *colorbutton;
+
+      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+
+      draw_area = drawing_area_new ();
+      gtk_container_add (GTK_CONTAINER (window), draw_area);
+
+      headerbar = gtk_header_bar_new ();
+      gtk_header_bar_set_title (GTK_HEADER_BAR (headerbar), "Paint");
+      gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (headerbar), TRUE);
+
+      colorbutton = gtk_color_button_new ();
+      g_signal_connect (colorbutton, "color-set",
+                        G_CALLBACK (color_button_color_set), draw_area);
+      gtk_color_chooser_set_rgba (GTK_COLOR_CHOOSER (colorbutton),
+                                  &(GdkRGBA) { 0, 0, 0, 1 });
+
+      gtk_header_bar_pack_end (GTK_HEADER_BAR (headerbar), colorbutton);
+      gtk_window_set_titlebar (GTK_WINDOW (window), headerbar);
+
+      g_signal_connect (window, "destroy",
+                        G_CALLBACK (gtk_widget_destroyed), &window);
+
+    }
+
+  if (!gtk_widget_get_visible (window))
+    gtk_widget_show (window);
+  else
+    gtk_widget_destroy (window);
+
+  return window;
+}