# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541869129 -3600
# Node ID 005f2f8e6a61464615bc3577e3ae74307ac8ef1f
# Parent  db91935dc4a635a070faf72a6d1580385f8d742e
Replaced the individual stored region abstraction with a collection abstraction,
permitting more convenient initialisation and introducing functions to obtain
image data and region positions. The storage state of regions is now managed by
a single counter of stored frames rather than a flag per frame.

diff -r db91935dc4a6 -r 005f2f8e6a61 examples/vga/main.c
--- a/examples/vga/main.c	Sat Nov 10 17:03:17 2018 +0100
+++ b/examples/vga/main.c	Sat Nov 10 17:58:49 2018 +0100
@@ -116,30 +116,43 @@
 
 /* Copy to the store from the display, then blit the image. */
 
-static void plot_sprite(stored_region_t *r, int x, int y, int key)
+static void plot_sprite(stored_regions_t *r, int x, int y, int key)
 {
-    display_copy(&display_config, r->image,
+    int frame = display_config.frame;
+    position_t *p = image_get_stored_position(r, frame);
+
+    /* Copy to the stored region. */
+
+    display_copy(&display_config, image_get_stored_region(r, frame),
                  sprite.width, sprite.height / SOURCE_YSTEP, 1,
                  x, y, -1, 0);
+
+    /* Plot to the screen. */
+
     display_copy(&display_config, sprite.image,
                  sprite.width, sprite.height, SOURCE_YSTEP,
                  x, y, key, 1);
 
-    /* Record the stored background. */
+    /* Record the stored background details. */
 
-    r->x = x;
-    r->y = y;
-    r->stored = 1;
+    p->x = x;
+    p->y = y;
+
+    if (frame >= r->stored)
+        r->stored = frame + 1;
 }
 
 /* Copy to the display from the store, restoring the original background. */
 
-static void unplot_sprite(stored_region_t *r)
+static void unplot_sprite(stored_regions_t *r)
 {
-    if (r->stored)
-        display_copy(&display_config, r->image,
+    int frame = display_config.frame;
+    position_t *p = image_get_stored_position(r, frame);
+
+    if (r->stored > frame)
+        display_copy(&display_config, image_get_stored_region(r, frame),
                      sprite.width, sprite.height / SOURCE_YSTEP, 1,
-                     r->x, r->y, -1, 1);
+                     p->x, p->y, -1, 1);
 }
 
 /* Plot the revealed region at the edge of the screen after scrolling. */
@@ -219,8 +232,7 @@
 {
     /* Stores of background details, replotted when moving the sprite. */
 
-    uint8_t backgrounds[FRAME_COUNT][(sprite.width * sprite.height) / SOURCE_YSTEP];
-    stored_region_t regions[FRAME_COUNT];
+    Stored_Regions(regions, FRAME_COUNT, (sprite.width * sprite.height) / SOURCE_YSTEP);
 
     /* Sprite position. */
 
@@ -244,9 +256,6 @@
     init_viewport(&v, &display_config, xorigins, yorigins,
                   SCROLL_XSTEP, SOURCE_YSTEP, plot_screen_edge);
 
-    init_stored_regions(regions, display_config.frames, (uint8_t *) backgrounds,
-                        (sprite.width * sprite.height) / SOURCE_YSTEP);
-
     /* Animation loop. */
 
     while (1)
@@ -255,7 +264,7 @@
         {
             for (x = 0; x < display_config.line_length - sprite.width; x++)
             {
-                plot_sprite(&regions[display_config.frame], x, y, 0x8c);
+                plot_sprite(&regions, x, y, 0x8c);
 
                 /* Update the display with the frame details. */
 
@@ -268,7 +277,7 @@
 
                 /* Prepare the frame for updates. */
 
-                unplot_sprite(&regions[display_config.frame]);
+                unplot_sprite(&regions);
 
                 /* Scroll in the indicated direction. */
 
diff -r db91935dc4a6 -r 005f2f8e6a61 include/image.h
--- a/include/image.h	Sat Nov 10 17:03:17 2018 +0100
+++ b/include/image.h	Sat Nov 10 17:58:49 2018 +0100
@@ -38,26 +38,52 @@
 
 } image_t;
 
+
+
 /* Stored display regions. */
 
 typedef struct
 {
+    /* Position of the stored region on the screen. */
+
+    int x, y;
+
+} position_t;
+
+typedef struct
+{
     /* Stored region overplotted by the sprite. */
 
     uint8_t *image;
+    uint32_t size;
+
+    /* Number of stored frames. */
+
     int stored;
 
-    /* Position of the stored region. */
+    /* Stored region positions. */
 
-    int x, y;
+    position_t *pos;
 
-} stored_region_t;
+} stored_regions_t;
 
 
 
-/* Initialise the stored regions. */
+/* Initialise stored regions, allocating memory and a structure to access it. */
 
-void init_stored_regions(stored_region_t *r, int frames,
-                         uint8_t *regions, uint32_t region_size);
+#define Stored_Regions(NAME, FRAMES, SIZE)      \
+    uint8_t __##NAME##_image[FRAMES * SIZE];    \
+    position_t __##NAME##_pos[FRAMES];          \
+    stored_regions_t NAME = {                   \
+        .image=__##NAME##_image,                \
+        .size=SIZE,                             \
+        .stored=0,                              \
+        .pos=__##NAME##_pos};
+
+/* Access functions. */
+
+position_t *image_get_stored_position(stored_regions_t *r, int frame);
+
+uint8_t *image_get_stored_region(stored_regions_t *r, int frame);
 
 #endif /* __IMAGE_H__ */
diff -r db91935dc4a6 -r 005f2f8e6a61 lib/image.c
--- a/lib/image.c	Sat Nov 10 17:03:17 2018 +0100
+++ b/lib/image.c	Sat Nov 10 17:58:49 2018 +0100
@@ -21,16 +21,16 @@
 
 
 
-void init_stored_regions(stored_region_t *r, int frames,
-                         uint8_t *regions, uint32_t region_size)
+/* Obtain the position for the stored region from the given frame. */
+
+position_t *image_get_stored_position(stored_regions_t *r, int frame)
 {
-    int frame;
+    return &r->pos[frame];
+}
 
-    for (frame = 0; frame < frames; frame++)
-    {
-        r->stored = 0;
-        r->image = regions;
-        regions += region_size;
-        r++;
-    }
+/* Obtain the image data for the stored region from the given frame. */
+
+uint8_t *image_get_stored_region(stored_regions_t *r, int frame)
+{
+    return r->image + r->size * frame;
 }