# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541351586 -3600
# Node ID 000b6b782bf4e8fb08d72291120128649643f8fa
# Parent  6d95b67997e657cdb4473d13ebffa2c4d83ea40c
Added support for source image scaling where images might be used in single- and
double-buffering modes.

diff -r 6d95b67997e6 -r 000b6b782bf4 examples/vga-timer/Makefile
--- a/examples/vga-timer/Makefile	Sun Nov 04 16:14:58 2018 +0100
+++ b/examples/vga-timer/Makefile	Sun Nov 04 18:13:06 2018 +0100
@@ -33,6 +33,6 @@
 # Application-specific adjustments.
 # See: examples/vga/Makefile
 
-CFLAGS += -DLINE_CHANNELS=2 -DTRANSFER_TIMER=3 -I../vga
+CFLAGS += -DLINE_CHANNELS=2 -DTRANSFER_TIMER=3 -DSOURCE_HEIGHT=128 -I../vga
 
 include ../../mk/rules.mk
diff -r 6d95b67997e6 -r 000b6b782bf4 examples/vga/main.c
--- a/examples/vga/main.c	Sun Nov 04 16:14:58 2018 +0100
+++ b/examples/vga/main.c	Sun Nov 04 18:13:06 2018 +0100
@@ -81,6 +81,16 @@
 
 
 
+/* Define the relationship between source images and the screen. */
+
+#ifndef SOURCE_HEIGHT
+#define SOURCE_HEIGHT   256
+#endif
+
+#define SOURCE_YSTEP    (SOURCE_HEIGHT / LINE_COUNT)
+
+
+
 /* Framebuffer memory. */
 
 static uint8_t framebuffer[FRAME_SIZE * FRAME_COUNT];
@@ -135,10 +145,10 @@
 static void plot_sprite(uint8_t *background, int x, int y)
 {
     copy_display(&display_config, background,
-                 sprite_width, sprite_height,
+                 sprite_width, sprite_height / SOURCE_YSTEP, 1,
                  x, y, -1, 0);
     copy_display(&display_config, sprite,
-                 sprite_width, sprite_height,
+                 sprite_width, sprite_height, SOURCE_YSTEP,
                  x, y, 0x8c, 1);
 }
 
@@ -147,7 +157,7 @@
 static void unplot_sprite(uint8_t *background, int x, int y)
 {
     copy_display(&display_config, background,
-                 sprite_width, sprite_height,
+                 sprite_width, sprite_height / SOURCE_YSTEP, 1,
                  x, y, -1, 1);
 }
 
@@ -177,6 +187,7 @@
                          screendata_width, screendata_height,
                          xsource, yorigin,
                          width, screendata_height - yorigin,
+                         SOURCE_YSTEP,
                          xdisplay, 0,
                          -1, 1);
 
@@ -190,7 +201,8 @@
                              screendata_width, screendata_height,
                              xsource, 0,
                              width, yorigin,
-                             xdisplay, screendata_height - yorigin,
+                             SOURCE_YSTEP,
+                             xdisplay, (screendata_height - yorigin) / SOURCE_YSTEP,
                              -1, 1);
 }
 
@@ -213,7 +225,7 @@
 {
     /* Stored region behind the sprite. */
 
-    uint8_t background[sprite_width * sprite_height];
+    uint8_t background[(sprite_width * sprite_height) / SOURCE_YSTEP];
 
     /* Sprite position. */
 
@@ -257,7 +269,8 @@
                 /* Update the vertical origin if appropriate. */
 
                 if (ydir)
-                    yorigin = wrap_value(yorigin + ydir, screendata_height);
+                    yorigin = wrap_value(yorigin + ydir * SOURCE_YSTEP,
+                                         screendata_height);
 
                 /* For horizontal scrolling, plot the exposed column at the left
                    (if scrolling left) or at the right (if scrolling right). */
@@ -326,9 +339,12 @@
 
         /* Plot the image centred on the screen. */
 
-        copy_display(&display_config, screendata, screendata_width, screendata_height,
+        copy_display(&display_config, screendata,
+                     screendata_width, screendata_height,
+                     SOURCE_YSTEP,
                      (display_config.line_length - screendata_width) / 2,
-                     (display_config.line_count - screendata_height) / 2, -1, 1);
+                     (display_config.line_count - (screendata_height / SOURCE_YSTEP)) / 2,
+                     -1, 1);
 
         /* Write a sequence of characters. */
 
diff -r 6d95b67997e6 -r 000b6b782bf4 include/display.h
--- a/include/display.h	Sun Nov 04 16:14:58 2018 +0100
+++ b/include/display.h	Sun Nov 04 18:13:06 2018 +0100
@@ -105,12 +105,13 @@
 
 void test_linedata(display_config_t *cfg);
 
-void copy_display(display_config_t *cfg, uint8_t *store, int width, int height,
+void copy_display(display_config_t *cfg, uint8_t *store,
+                  int width, int height, int ystep,
                   int x, int y, int key, int to_display);
 
 void copy_display_section(display_config_t *cfg, uint8_t *store,
                   int width, int height,
-                  int xstart, int ystart, int xsize, int ysize,
+                  int xstart, int ystart, int xsize, int ysize, int ystep,
                   int x, int y, int key, int to_display);
 
 void scroll_display(display_config_t *cfg, int x, int y);
diff -r 6d95b67997e6 -r 000b6b782bf4 lib/display.c
--- a/lib/display.c	Sun Nov 04 16:14:58 2018 +0100
+++ b/lib/display.c	Sun Nov 04 18:13:06 2018 +0100
@@ -153,18 +153,20 @@
 
 /* Copying from/to the display to/from a backing store. */
 
-void copy_display(display_config_t *cfg, uint8_t *store, int width, int height,
+void copy_display(display_config_t *cfg, uint8_t *store,
+                  int width, int height, int ystep,
                   int x, int y, int key, int to_display)
 {
-    copy_display_section(cfg, store, width, height, 0, 0, width, height, x, y,
-                         key, to_display);
+    copy_display_section(cfg, store, width, height,
+                         0, 0, width, height, ystep,
+                         x, y, key, to_display);
 }
 
 /* Copying from/to the display to/from a backing store region. */
 
 void copy_display_section(display_config_t *cfg, uint8_t *store,
                           int width, int height,
-                          int xstart, int ystart, int xsize, int ysize,
+                          int xstart, int ystart, int xsize, int ysize, int ystep,
                           int x, int y, int key, int to_display)
 {
     int sx, sy, dx, dy;
@@ -184,7 +186,7 @@
 
     /* Perform the copying between the store and display. */
 
-    for (sy = ystart, dy = y; (sy < ylimit) && (dy < cfg->line_count); sy++, dy++)
+    for (sy = ystart, dy = y; (sy < ylimit) && (dy < cfg->line_count); sy += ystep, dy++)
     {
         for (sx = xstart, dx = x; (sx < xlimit) && (dx < cfg->line_length); sx++, dx++)
         {
@@ -198,7 +200,7 @@
                 storeline[sx] = displayline[get_position(cfg, dx)];
         }
 
-        storeline += width;
+        storeline += width * ystep;
         displayline = wrap_screen_pointer(cfg, displayline + cfg->line_length);
     }
 }