# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1542118657 -3600
# Node ID ea0474d3418207040aebf08f5ccea9310ac140d9
# Parent  f98c32b8cbb73e00042abc55fdcd629948207a1a
Added support for unplotting sprites using the viewport and background image.

diff -r f98c32b8cbb7 -r ea0474d34182 examples/vga/main.c
--- a/examples/vga/main.c	Tue Nov 13 14:35:22 2018 +0100
+++ b/examples/vga/main.c	Tue Nov 13 15:17:37 2018 +0100
@@ -162,7 +162,7 @@
 
                 /* Prepare the frame for updates. */
 
-                image_unplot_sprite(&s);
+                viewport_unplot_sprite_from_image(&v, &s, &scr);
 
                 /* Scroll in the indicated direction. */
 
diff -r f98c32b8cbb7 -r ea0474d34182 include/image.h
--- a/include/image.h	Tue Nov 13 14:35:22 2018 +0100
+++ b/include/image.h	Tue Nov 13 15:17:37 2018 +0100
@@ -152,6 +152,9 @@
 
 void image_unplot_sprite(sprite_t *s);
 
+void image_unplot_sprite_from_image(sprite_t *s, sprite_t *bg,
+                                    int xorigin, int yorigin);
+
 /* Convenience operations. */
 
 void image_plot_sprite_section(sprite_t *s,
@@ -165,4 +168,8 @@
 void image_update_scrolled_tiled_image(sprite_t *s, int xorigin, int yorigin,
                                                     int xstep, int ystep);
 
+void image_update_tiled_image(sprite_t *s, int xorigin, int yorigin,
+                                           int width, int height,
+                                           int xdisplay, int ydisplay);
+
 #endif /* __IMAGE_H__ */
diff -r f98c32b8cbb7 -r ea0474d34182 include/viewport.h
--- a/include/viewport.h	Tue Nov 13 14:35:22 2018 +0100
+++ b/include/viewport.h	Tue Nov 13 15:17:37 2018 +0100
@@ -21,6 +21,7 @@
 #define __VIEWPORT_H__
 
 #include "display.h"
+#include "image.h"
 
 
 
@@ -77,4 +78,8 @@
 
 void viewport_update_origin(viewport_t *v, int dx, int dy);
 
+/* Update operations. */
+
+void viewport_unplot_sprite_from_image(viewport_t *v, sprite_t *s, sprite_t *bg);
+
 #endif /* __VIEWPORT_H__ */
diff -r f98c32b8cbb7 -r ea0474d34182 lib/image.c
--- a/lib/image.c	Tue Nov 13 14:35:22 2018 +0100
+++ b/lib/image.c	Tue Nov 13 15:17:37 2018 +0100
@@ -98,6 +98,23 @@
                      p->x, p->y, -1, 1);
 }
 
+/* Unplot a sprite by restoring a region from the background image. */
+
+void image_unplot_sprite_from_image(sprite_t *s, sprite_t *bg,
+                                    int xorigin, int yorigin)
+{
+    int frame = s->cfg->frame;
+    position_t *p = image_get_stored_position(s, frame);
+
+    /* Plot the region of the background using the sprite image dimensions
+       converted to background image dimensions at the sprite's position on the
+       display. */
+
+    image_update_tiled_image(bg, xorigin, yorigin,
+                             s->image->width, (s->image->height / s->yscale) * bg->yscale,
+                             p->x, p->y);
+}
+
 
 
 /* Plot a section of an image without storing the background beforehand. */
@@ -233,3 +250,21 @@
                           0, ydisplay);
     }
 }
+
+/* Plot a region of a tiled image. */
+
+void image_update_tiled_image(sprite_t *s, int xorigin, int yorigin,
+                                           int width, int height,
+                                           int xdisplay, int ydisplay)
+{
+    /* Find the source position for the region. */
+
+    int xsource = wrap_value(xorigin + xdisplay, s->image->width);
+    int ysource = wrap_value(yorigin + ydisplay * s->yscale, s->image->height);
+
+    /* Request tiling in the source coordinates. */
+
+    image_tile_sprite(s, xsource, ysource,
+                      width, height,
+                      xdisplay, ydisplay);
+}
diff -r f98c32b8cbb7 -r ea0474d34182 lib/viewport.c
--- a/lib/viewport.c	Tue Nov 13 14:35:22 2018 +0100
+++ b/lib/viewport.c	Tue Nov 13 15:17:37 2018 +0100
@@ -72,3 +72,12 @@
     v->xorigins[frame] = v->xorigin;
     v->yorigins[frame] = v->yorigin;
 }
+
+/* Update the display, unplotting a sprite and replotting the background. */
+
+void viewport_unplot_sprite_from_image(viewport_t *v, sprite_t *s, sprite_t *bg)
+{
+    int frame = v->cfg->frame;
+
+    image_unplot_sprite_from_image(s, bg, v->xorigins[frame], v->yorigins[frame]);
+}