# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1542130747 -3600
# Node ID 79f53d89a0fd0570f6765cfadaa008f911fcb7b3
# Parent  ddb4b7db1d9bb48f32927007d836b30343647b7d
Demonstrate multiple sprites moving around at the same time.

diff -r ddb4b7db1d9b -r 79f53d89a0fd examples/vga/main.c
--- a/examples/vga/main.c	Tue Nov 13 17:54:21 2018 +0100
+++ b/examples/vga/main.c	Tue Nov 13 18:39:07 2018 +0100
@@ -112,26 +112,47 @@
 
 
 
+/* Update the sprite position. */
+
+static void update_sprite_position(sprite_t *s, int *xdir, int *ydir)
+{
+    position_t *last = image_get_stored_position(s, wrap_value(display_config.frame - 1, display_config.frames));
+    position_t *next = image_get_sprite_position(s);
+
+    if (((*xdir > 0) && (last->x < display_config.line_length - s->image->width - *xdir)) ||
+        ((*xdir < 0) && (last->x > -*xdir)))
+    {
+        next->x = last->x + *xdir;
+    }
+    else
+    {
+        next->x = last->x;
+        if (*xdir)
+            *xdir = -*xdir;
+    }
+
+    if (((*ydir > 0) && (last->y < display_config.line_count - s->image->height / s->yscale - *ydir)) ||
+        ((*ydir < 0) && (last->y > -*ydir)))
+    {
+        next->y = last->y + *ydir;
+    }
+    else
+    {
+        next->y = last->y;
+        if (*ydir)
+            *ydir = -*ydir;
+    }
+}
+
 /* Move a sprite around on the framebuffer. */
 
 static void animate(uint32_t delay)
 {
     /* Stores of background details, replotted when moving the sprite. */
 
-    Sprite(s, &sprite, &display_config, FRAME_COUNT, 0x0c, SOURCE_YSTEP);
-
-    /* Sprite position. */
-
-    int x, y;
-
-    /* Scrolling directions. */
-
-    int dir[] = {1, 0, -1, 0, 1};
-    int dirindex = 0;
-
-    /* Scroll increments. */
-
-    int xdir, ydir;
+    Sprite(s1, &sprite, &display_config, FRAME_COUNT, 0x0c, SOURCE_YSTEP);
+    Sprite(s2, &sprite, &display_config, FRAME_COUNT, 0x0c, SOURCE_YSTEP);
+    Sprite(s3, &sprite, &display_config, FRAME_COUNT, 0x0c, SOURCE_YSTEP);
 
     /* Scrolling viewport. */
 
@@ -141,53 +162,57 @@
 
     viewport_set_origin(&v, 0, 0);
 
+    /* Sprite and scrolling directions. */
+
+    int xdir[] = {1, -1, 0}, ydir[] = {1, 0, -1};
+
+    /* Sprite positions. */
+
+    image_set_sprite_position(&s1, 0, 0);
+    image_set_sprite_position(&s2, display_config.line_length - s2.image->width, 0);
+    image_set_sprite_position(&s3, 0, display_config.line_count - s3.image->height);
+
     /* Animation loop. */
 
     while (1)
     {
-        for (y = 0; y < display_config.line_count - s.image->height; y++)
-        {
-            for (x = 0; x < display_config.line_length - s.image->width; x++)
-            {
-                image_set_sprite_position(&s, x, y);
-                image_plot_sprite(&s);
+        image_plot_sprite(&s1);
+        image_plot_sprite(&s2);
+        image_plot_sprite(&s3);
 
-                /* Update the display with the frame details. */
+        /* Update the display with the frame details. */
+
+        vga_set_frame(&display_config, 1);
+        wait(delay);
 
-                vga_set_frame(&display_config, 1);
-                wait(delay);
+        /* Select the next frame to plot to. */
 
-                /* Select the next frame to plot to. */
+        display_select_next_frame(&display_config);
 
-                display_select_next_frame(&display_config);
-
-                /* Prepare the frame for updates. */
+        /* Prepare the frame for updates. */
 
-                viewport_unplot_sprite_from_image(&v, &s, &scr);
-
-                /* Scroll in the indicated direction. */
+        viewport_unplot_sprite_from_image(&v, &s1, &scr);
+        viewport_unplot_sprite_from_image(&v, &s2, &scr);
+        viewport_unplot_sprite_from_image(&v, &s3, &scr);
 
-                xdir = dir[dirindex];
-                ydir = dir[dirindex + 1];
-
-                /* Update the origin if appropriate. */
+        /* Update the origin to scroll the screen. */
 
-                /* Due to the effect of a simple screen start increment in the
-                   dual channel configuration, horizontal scrolling involves two
-                   pixel increments and thus requires a two-pixel column to be
-                   plotted per scrolling increment. */
+        /* Due to the effect of a simple screen start increment in the
+           dual channel configuration, horizontal scrolling involves two
+           pixel increments and thus requires a two-pixel column to be
+           plotted per scrolling increment. */
 
-                /* For vertically-scaled backgrounds, the full resolution image
-                   is traversed by multiples of the scrolling increment. */
+        /* For vertically-scaled backgrounds, the full resolution image
+           is traversed by multiples of the scrolling increment. */
+
+        viewport_update_origin(&v, xdir[0] * SCROLL_XSTEP,
+                                   ydir[0] * SOURCE_YSTEP);
 
-                viewport_update_origin(&v, xdir * SCROLL_XSTEP,
-                                           ydir * SOURCE_YSTEP);
-            }
+        /* Update the position of the sprite being plotted. */
 
-            /* Switch direction periodically. */
-
-            dirindex = wrap_value(dirindex + 1, 4);
-        }
+        update_sprite_position(&s1, &xdir[0], &ydir[0]);
+        update_sprite_position(&s2, &xdir[1], &ydir[1]);
+        update_sprite_position(&s3, &xdir[2], &ydir[2]);
     }
 }
 
@@ -292,7 +317,7 @@
     /* Move a sprite around on the screen with a delay between each movement. */
 
     setup();
-    animate(1 << 18);
+    animate(1);
 }