[gnome-commander] InternalViewer: Implement scrolling via keyboard arrow keys, partly fixing #95

[Uwe Scholz <uwescholz src gnome org>]

commit 3495339399ed05b0cacce45fe2e967df1ac10dcd
Author: Uwe Scholz <u scholz83 gmx de>
Date:   Sat Feb 13 22:44:55 2021 +0100

    InternalViewer: Implement scrolling via keyboard arrow keys, partly fixing #95

 src/intviewer/image-render.cc | 86 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
---
diff --git a/src/intviewer/image-render.cc b/src/intviewer/image-render.cc
index e60ca7a3..8b708b42 100644
--- a/src/intviewer/image-render.cc
+++ b/src/intviewer/image-render.cc
@@ -45,6 +45,7 @@ using namespace std;
 
 #define IMAGE_RENDER_DEFAULT_WIDTH      100
 #define IMAGE_RENDER_DEFAULT_HEIGHT     200
+#define INC_VALUE 25.0
 
 
 enum {
@@ -124,6 +125,17 @@ static void image_render_update_adjustments (ImageRender *obj);
     public functions
     (defined in the header file)
 *****************************************/
+GtkAdjustment *image_render_get_h_adjustment (ImageRender *obj)
+{
+    g_return_val_if_fail (IS_IMAGE_RENDER(obj), nullptr);
+
+    if (obj->priv->h_adjustment)
+    {
+        return obj->priv->h_adjustment;
+    }
+    return nullptr;
+}
+
 void image_render_set_h_adjustment (ImageRender *obj, GtkAdjustment *adjustment)
 {
     g_return_if_fail (IS_IMAGE_RENDER(obj));
@@ -148,6 +160,17 @@ void image_render_set_h_adjustment (ImageRender *obj, GtkAdjustment *adjustment)
 }
 
 
+GtkAdjustment *image_render_get_v_adjustment (ImageRender *obj)
+{
+    g_return_val_if_fail (IS_IMAGE_RENDER(obj), nullptr);
+
+    if (obj->priv->v_adjustment)
+    {
+        return obj->priv->v_adjustment;
+    }
+    return nullptr;
+}
+
 void image_render_set_v_adjustment (ImageRender *obj, GtkAdjustment *adjustment)
 {
     g_return_if_fail (IS_IMAGE_RENDER(obj));
@@ -293,6 +316,69 @@ void image_render_notify_status_changed (ImageRender *w)
 
 static gboolean image_render_key_press (GtkWidget *widget, GdkEventKey *event)
 {
+    g_return_val_if_fail (IS_IMAGE_RENDER (widget), FALSE);
+
+    auto imageRender = IMAGE_RENDER (widget);
+
+    switch (event->keyval)
+    {
+        case GDK_KEY_Up:
+        {
+            auto vAdjustment = image_render_get_v_adjustment(imageRender);
+            auto current = gtk_adjustment_get_value(vAdjustment);
+            auto lower = gtk_adjustment_get_lower(vAdjustment);
+            if (current > lower)
+            {
+                gtk_adjustment_set_value(vAdjustment, current - INC_VALUE);
+            }
+            return TRUE;
+        }
+        case GDK_KEY_Down:
+        {
+            auto vAdjustment = image_render_get_v_adjustment(imageRender);
+            auto current = gtk_adjustment_get_value(vAdjustment);
+            auto upper = gtk_adjustment_get_upper(vAdjustment);
+            auto page_size = gtk_adjustment_get_page_size(vAdjustment);
+            if (current < upper - page_size)
+            {
+                gtk_adjustment_set_value(vAdjustment, current + INC_VALUE);
+            }
+            return TRUE;
+        }
+        case GDK_KEY_Left:
+        {
+            auto hAdjustment = image_render_get_h_adjustment(imageRender);
+            auto current = gtk_adjustment_get_value(hAdjustment);
+            auto lower = gtk_adjustment_get_lower(hAdjustment);
+            if (current > lower)
+            {
+                gtk_adjustment_set_value(hAdjustment, current - INC_VALUE);
+            }
+            return TRUE;
+        }
+        case GDK_KEY_Right:
+        {
+            auto hAdjustment = image_render_get_h_adjustment(imageRender);
+            auto current = gtk_adjustment_get_value(hAdjustment);
+            auto upper = gtk_adjustment_get_upper(hAdjustment);
+            auto page_size = gtk_adjustment_get_page_size(hAdjustment);
+            if (current < upper - page_size)
+            {
+                gtk_adjustment_set_value(hAdjustment, current + INC_VALUE);
+            }
+            return TRUE;
+        }
+
+        default:
+           break;
+    }
+
+    switch (state_is_blank(event->keyval))
+    {
+        default:
+           break;
+    }
+
     return FALSE;
 }