# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541971420 -3600
# Node ID c8bb3228030dcbe7455dc88e5b8de57da359f500
# Parent  14bc79b7e4dc9af5c34459412116a0340bd9302c
Moved the function for updating a tiled image background to the image module.

diff -r 14bc79b7e4dc -r c8bb3228030d examples/vga/main.c
--- a/examples/vga/main.c	Sun Nov 11 18:15:24 2018 +0100
+++ b/examples/vga/main.c	Sun Nov 11 22:23:40 2018 +0100
@@ -107,57 +107,7 @@
 
 static void plot_screen_edge(int xorigin, int yorigin, int xstep, int ystep)
 {
-    /* The display regions are either the left or right edge... */
-
-    int xedge = xstep < 0 ? 0 : display_config.line_length - xstep;
-    int xdisplay = xedge;
-
-    /* and either the top or bottom edge... */
-
-    int yedge = ystep < 0 ? 0 : display_config.line_count * scr.yscale - ystep;
-    int ydisplay = yedge / scr.yscale;
-
-    /* Determine the origin position within the image. */
-
-    int xpos = wrap_value(xorigin, scr.image->width);
-    int ypos = wrap_value(yorigin, scr.image->height);
-    int xsource, ysource;
-
-    /* Horizontal scrolling requires columns spanning the height of the screen
-       at the appropriate edge (left or right). */
-
-    /* The column width is the absolute increment. */
-
-    if (xstep)
-    {
-        /* Find the source position for the appropriate edge. */
-
-        xsource = wrap_value(xpos + xedge, scr.image->width);
-        ysource = ypos;
-
-        /* Request tiling in the source coordinates. */
-
-        image_tile_sprite(&scr, xsource, ysource,
-                          abs(xstep), display_config.line_count * scr.yscale,
-                          xdisplay, 0);
-    }
-
-    /* Vertical scrolling requires columns across the width of the screen at the
-       appropriate edge (top or bottom). */
-
-    if (ystep)
-    {
-        /* Find the source position for the appropriate edge. */
-
-        xsource = xpos;
-        ysource = wrap_value(ypos + yedge, scr.image->height);
-
-        /* Request tiling in the source coordinates. */
-
-        image_tile_sprite(&scr, xsource, ysource,
-                          display_config.line_length, abs(ystep),
-                          0, ydisplay);
-    }
+    image_update_scrolled_tiled_image(&scr, xorigin, yorigin, xstep, ystep);
 }
 
 
diff -r 14bc79b7e4dc -r c8bb3228030d include/image.h
--- a/include/image.h	Sun Nov 11 18:15:24 2018 +0100
+++ b/include/image.h	Sun Nov 11 22:23:40 2018 +0100
@@ -160,4 +160,7 @@
                                     int width, int height,
                                     int xdisplay, int ydisplay);
 
+void image_update_scrolled_tiled_image(sprite_t *s, int xorigin, int yorigin,
+                                                    int xstep, int ystep);
+
 #endif /* __IMAGE_H__ */
diff -r 14bc79b7e4dc -r c8bb3228030d lib/image.c
--- a/lib/image.c	Sun Nov 11 18:15:24 2018 +0100
+++ b/lib/image.c	Sun Nov 11 22:23:40 2018 +0100
@@ -175,3 +175,61 @@
         source_width = s->image->width;
     }
 }
+
+/* Plot a scrolling tiled image upon a viewport update. */
+
+void image_update_scrolled_tiled_image(sprite_t *s, int xorigin, int yorigin,
+                                                    int xstep, int ystep)
+{
+    /* The display regions are either the left or right edge... */
+
+    int xedge = xstep < 0 ? 0 : s->cfg->line_length - xstep;
+    int xdisplay = xedge;
+
+    /* and either the top or bottom edge... */
+
+    int yedge = ystep < 0 ? 0 : s->cfg->line_count * s->yscale - ystep;
+    int ydisplay = yedge / s->yscale;
+
+    /* Determine the origin position within the image. */
+
+    int xpos = wrap_value(xorigin, s->image->width);
+    int ypos = wrap_value(yorigin, s->image->height);
+    int xsource, ysource;
+
+    /* Horizontal scrolling requires columns spanning the height of the screen
+       at the appropriate edge (left or right). */
+
+    /* The column width is the absolute increment. */
+
+    if (xstep)
+    {
+        /* Find the source position for the appropriate edge. */
+
+        xsource = wrap_value(xpos + xedge, s->image->width);
+        ysource = ypos;
+
+        /* Request tiling in the source coordinates. */
+
+        image_tile_sprite(s, xsource, ysource,
+                          abs(xstep), s->cfg->line_count * s->yscale,
+                          xdisplay, 0);
+    }
+
+    /* Vertical scrolling requires columns across the width of the screen at the
+       appropriate edge (top or bottom). */
+
+    if (ystep)
+    {
+        /* Find the source position for the appropriate edge. */
+
+        xsource = xpos;
+        ysource = wrap_value(ypos + yedge, s->image->height);
+
+        /* Request tiling in the source coordinates. */
+
+        image_tile_sprite(s, xsource, ysource,
+                          s->cfg->line_length, abs(ystep),
+                          0, ydisplay);
+    }
+}