# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541886006 -3600
# Node ID 2cf83f9160baa9fba13abbb1111ae0f6420aa67c
# Parent  f1ce70172578685b93718dc1d3c5c4584fd369a8
Introduced a simplified sprite variant for convenience.

diff -r f1ce70172578 -r 2cf83f9160ba examples/vga/main.c
--- a/examples/vga/main.c	Sat Nov 10 22:11:32 2018 +0100
+++ b/examples/vga/main.c	Sat Nov 10 22:40:06 2018 +0100
@@ -281,6 +281,7 @@
 
 static void setup(void)
 {
+    SpriteOverwriting(scr, &screendata, &display_config, SOURCE_YSTEP);
     int frame;
 
     for (frame = 0; frame < display_config.frames; frame++)
@@ -291,12 +292,10 @@
 
         /* Plot the image centred on the screen. */
 
-        display_copy(&display_config, screendata.image,
-                     screendata.width, screendata.height,
-                     SOURCE_YSTEP,
-                     (display_config.line_length - screendata.width) / 2,
-                     (display_config.line_count - (screendata.height / SOURCE_YSTEP)) / 2,
-                     -1, 1);
+        image_plot_sprite(&scr,
+            (display_config.line_length - scr.image->width) / 2,
+            (display_config.line_count - (scr.image->height / scr.yscale)) / 2,
+            -1);
 
         /* Write a sequence of characters. */
 
diff -r f1ce70172578 -r 2cf83f9160ba include/image.h
--- a/include/image.h	Sat Nov 10 22:11:32 2018 +0100
+++ b/include/image.h	Sat Nov 10 22:40:06 2018 +0100
@@ -116,6 +116,19 @@
 
 
 
+/* Initialise a sprite object using an existing image without the capability of
+   storing regions of the screen.
+
+   SpriteOverwriting(<name>, image_t *image, display_config_t *cfg, int yscale)
+*/
+
+#define SpriteOverwriting(NAME, IMAGE, CFG, YSCALE)                 \
+    sprite_t NAME = {                                               \
+        .image=IMAGE,                                               \
+        .regions=0,                                                 \
+        .yscale=YSCALE,                                             \
+        .cfg=CFG};
+
 /* Initialise a sprite object using an existing image, creating stored regions
    for the animation of the sprite.
 
diff -r f1ce70172578 -r 2cf83f9160ba lib/image.c
--- a/lib/image.c	Sat Nov 10 22:11:32 2018 +0100
+++ b/lib/image.c	Sat Nov 10 22:40:06 2018 +0100
@@ -42,14 +42,20 @@
 
 void image_plot_sprite(sprite_t *s, int x, int y, int key)
 {
-    int frame = s->cfg->frame;
-    position_t *p = image_get_stored_position(s->regions, frame);
+    int frame = 0;
+    position_t *p = 0;
 
-    /* Copy to the stored region. */
+    if (s->regions)
+    {
+        frame = s->cfg->frame;
+        p = image_get_stored_position(s->regions, frame);
 
-    display_copy(s->cfg, image_get_stored_region(s->regions, frame),
-                 s->image->width, s->image->height / s->yscale, 1,
-                 x, y, -1, 0);
+        /* Copy to the stored region. */
+
+        display_copy(s->cfg, image_get_stored_region(s->regions, frame),
+                     s->image->width, s->image->height / s->yscale, 1,
+                     x, y, -1, 0);
+    }
 
     /* Plot to the screen. */
 
@@ -57,13 +63,16 @@
                  s->image->width, s->image->height, s->yscale,
                  x, y, key, 1);
 
-    /* Record the stored background details. */
+    if (s->regions)
+    {
+        /* Record the stored background details. */
 
-    p->x = x;
-    p->y = y;
+        p->x = x;
+        p->y = y;
 
-    if (frame >= s->regions->stored)
-        s->regions->stored = frame + 1;
+        if (frame >= s->regions->stored)
+            s->regions->stored = frame + 1;
+    }
 }
 
 /* Copy a region from the store to the screen, restoring the original
@@ -71,8 +80,14 @@
 
 void image_unplot_sprite(sprite_t *s)
 {
-    int frame = s->cfg->frame;
-    position_t *p = image_get_stored_position(s->regions, frame);
+    int frame;
+    position_t *p;
+
+    if (!s->regions)
+        return;
+
+    frame = s->cfg->frame;
+    p = image_get_stored_position(s->regions, frame);
 
     /* Only unplot the sprite if a region was stored for the frame. */