Added an overload of draw_image() that's useful for drawing images

and doing interpolation at the same time.

dlib/gui_widgets/canvas_drawing.h

@@ -695,6 +695,37 @@ namespace dlib
         }
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename image_type 
+        >
+    void draw_image (
+        const canvas& c,
+        const rectangle& rect,
+        const image_type& img,
+        const rectangle& area_ = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
+                                          std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
+    )
+    {
+        const rectangle area = c.intersect(rect).intersect(area_);
+        if (area.is_empty() || img.size() == 0)
+            return;
+
+        const matrix<long,1> x = matrix_cast<long>(round(linspace(0, img.nc()-1, rect.width())));
+        const matrix<long,1> y = matrix_cast<long>(round(linspace(0, img.nr()-1, rect.height())));
+
+        for (long row = area.top(); row <= area.bottom(); ++row)
+        {
+            const long r = y(row-rect.top());
+            long cc = area.left() - rect.left();
+            for (long col = area.left(); col <= area.right(); ++col)
+            {
+                assign_pixel(c[row-c.top()][col-c.left()], img[r][x(cc++)]);
+            }
+        }
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <typename pixel_type>

dlib/gui_widgets/canvas_drawing_abstract.h

@@ -240,6 +240,33 @@ namespace dlib
             - only draws the part of the image that overlaps with the area rectangle
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename image_type 
+        >
+    void draw_image (
+        const canvas& c,
+        const rectangle& rect,
+        const image_type& img,
+        const rectangle& area = rectangle(-infinity,-infinity,infinity,infinity)
+    );
+    /*!
+        requires
+            - image_type == an implementation of array2d/array2d_kernel_abstract.h
+            - pixel_traits<typename image_type::type> is defined
+        ensures
+            - draws the given image object onto the canvas such that the upper left corner
+              of the image will appear at the point rect.tl_corner() in the canvas's window
+              and the lower right corner of the image will appear at rect.br_corner() in
+              the canvas's window.  (note that the upper left corner of the image is
+              assumed to be the pixel image[0][0] and the lower right corner of the image
+              is assumed to be image[image.nr()-1][image.nc()-1])
+            - only draws the part of the image that overlaps with the area rectangle
+            - Uses nearest neighbor interpolation when the given rect isn't the same size
+              as the input image.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <