# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541889489 -3600
# Node ID 301fb9b9ed234e8e4e4390a2640f598c16491dd5
# Parent  a695872c3adb0bf94d32371c5cd40af5b771919f
Introduced partial sprite plotting into the screen edge update function.

diff -r a695872c3adb -r 301fb9b9ed23 examples/vga/main.c
--- a/examples/vga/main.c	Sat Nov 10 23:00:40 2018 +0100
+++ b/examples/vga/main.c	Sat Nov 10 23:38:09 2018 +0100
@@ -93,6 +93,8 @@
 extern image_t screendata;
 extern image_t sprite;
 
+static SpriteOverwriting(scr, &screendata, &display_config, SOURCE_YSTEP);
+
 extern uint8_t fontchars[];
 extern uint32_t fonttable[];
 extern uint32_t fontbase, fontlimit;
@@ -108,16 +110,16 @@
 {
     /* Determine positions within the image. */
 
-    int xpos = wrap_value(xorigin, screendata.width);
-    int ypos = wrap_value(yorigin, screendata.height);
+    int xpos = wrap_value(xorigin, scr.image->width);
+    int ypos = wrap_value(yorigin, scr.image->height);
 
     /* The display region is either the left or right edge. */
 
-    int xdisplay = xstep < 0 ? 0 : screendata.width - xstep;
+    int xdisplay = xstep < 0 ? 0 : scr.image->width - xstep;
 
     /* The source region depends on the origin within the background image. */
 
-    int xsource = wrap_value(xdisplay + xpos, screendata.width);
+    int xsource = wrap_value(xdisplay + xpos, scr.image->width);
 
     /* The column width is the absolute increment. */
 
@@ -126,7 +128,7 @@
     /* Not all of the column may be available if close to the edge of the
        image, requiring multiple slices. */
 
-    int available = screendata.width - xsource;
+    int available = scr.image->width - xsource;
 
     while (width)
     {
@@ -136,13 +138,10 @@
            upwards (or downwards having wrapped around) on the
            screen. */
 
-        display_copy_section(&display_config, screendata.image,
-                             screendata.width, screendata.height,
-                             xsource, ypos,
-                             width, screendata.height - ypos,
-                             v->yscale,
-                             xdisplay, 0,
-                             -1, 1);
+        image_plot_sprite_section(&scr, xsource, ypos,
+                                  width, scr.image->height - ypos,
+                                  xdisplay, 0,
+                                  -1);
 
         /* The second column is at (xdisplay, h - ypos) and
            provides the upper part of the background image displaced
@@ -150,13 +149,10 @@
            screen. */
 
         if (ypos)
-            display_copy_section(&display_config, screendata.image,
-                                 screendata.width, screendata.height,
-                                 xsource, 0,
-                                 width, ypos,
-                                 v->yscale,
-                                 xdisplay, (screendata.height - ypos) / v->yscale,
-                                 -1, 1);
+            image_plot_sprite_section(&scr, xsource, 0,
+                                      width, ypos,
+                                      xdisplay, (scr.image->height - ypos) / v->yscale,
+                                      -1);
 
         /* Get the next slice of the column. */
 
@@ -164,8 +160,8 @@
         {
             width -= available;
             xsource = 0;
-            xdisplay = wrap_value(xdisplay + available, screendata.width);
-            available = screendata.width;
+            xdisplay = wrap_value(xdisplay + available, scr.image->width);
+            available = scr.image->width;
         }
         else
             width = 0;
@@ -281,7 +277,6 @@
 
 static void setup(void)
 {
-    SpriteOverwriting(scr, &screendata, &display_config, SOURCE_YSTEP);
     int frame;
 
     for (frame = 0; frame < display_config.frames; frame++)
diff -r a695872c3adb -r 301fb9b9ed23 include/image.h
--- a/include/image.h	Sat Nov 10 23:00:40 2018 +0100
+++ b/include/image.h	Sat Nov 10 23:38:09 2018 +0100
@@ -144,10 +144,16 @@
         .yscale=YSCALE,                                             \
         .cfg=CFG};
 
-/* Plotting operations. */
+/* Sprite plotting operations. */
 
 void image_plot_sprite(sprite_t *s, int x, int y, int key);
 
 void image_unplot_sprite(sprite_t *s);
 
+/* Convenience operations. */
+
+void image_plot_sprite_section(sprite_t *s,
+                               int xstart, int ystart, int xsize, int ysize,
+                               int x, int y, int key);
+
 #endif /* __IMAGE_H__ */
diff -r a695872c3adb -r 301fb9b9ed23 lib/image.c
--- a/lib/image.c	Sat Nov 10 23:00:40 2018 +0100
+++ b/lib/image.c	Sat Nov 10 23:38:09 2018 +0100
@@ -96,3 +96,17 @@
                      s->image->width, s->image->height / s->yscale, 1,
                      p->x, p->y, -1, 1);
 }
+
+
+
+/* Plot a section of an image without storing the background beforehand. */
+
+void image_plot_sprite_section(sprite_t *s,
+                               int xstart, int ystart, int xsize, int ysize,
+                               int x, int y, int key)
+{
+    display_copy_section(s->cfg, s->image->image,
+                         s->image->width, s->image->height,
+                         xstart, ystart, xsize, ysize, s->yscale,
+                         x, y, key, 1);
+}