1.1 --- a/examples/vga/main.c Wed Oct 31 18:02:07 2018 +0100
1.2 +++ b/examples/vga/main.c Thu Nov 01 19:28:53 2018 +0100
1.3 @@ -114,7 +114,7 @@
1.4 uint8_t background[sprite_width * sprite_height];
1.5 int x, y;
1.6 int dir[] = {1, 0, -1, 0, 1}, i = 0, width, column_width;
1.7 - int xsource, xdisplay, xorigin = 0;
1.8 + int xsource, xdisplay, xorigin = 0, yorigin = 0;
1.9
1.10 while (1)
1.11 {
1.12 @@ -144,6 +144,18 @@
1.13
1.14 scroll_display(&display_config, dir[i], dir[i + 1]);
1.15
1.16 + /* Update the vertical origin if appropriate. */
1.17 +
1.18 + if (dir[i + 1])
1.19 + {
1.20 + yorigin += dir[i + 1];
1.21 +
1.22 + if (yorigin < 0)
1.23 + yorigin += screendata_height;
1.24 + else if (yorigin >= screendata_height)
1.25 + yorigin -= screendata_height;
1.26 + }
1.27 +
1.28 /* For horizontal scrolling, plot the exposed column at the left
1.29 (if scrolling left) or at the right (if scrolling right). */
1.30
1.31 @@ -164,14 +176,39 @@
1.32 /* Determine the location of the column to be plotted. */
1.33
1.34 xorigin += width;
1.35 +
1.36 + if (xorigin < 0)
1.37 + xorigin += screendata_width;
1.38 + else if (xorigin >= screendata_width)
1.39 + xorigin -= screendata_width;
1.40 +
1.41 xsource = (xdisplay + xorigin) % screendata_width;
1.42
1.43 + /* Plot a column in two pieces if the vertical origin is
1.44 + non-zero. The first piece is at (xdisplay, 0) and
1.45 + provides the lower part of the background image displaced
1.46 + upwards (or downwards having wrapped around) on the
1.47 + screen. */
1.48 +
1.49 copy_display_section(&display_config, screendata,
1.50 screendata_width, screendata_height,
1.51 - xsource, 0,
1.52 - column_width, screendata_height,
1.53 + xsource, yorigin,
1.54 + column_width, screendata_height - yorigin,
1.55 xdisplay, 0,
1.56 -1, 1);
1.57 +
1.58 + /* The second column is at (xdisplay, h - yorigin) and
1.59 + provides the upper part of the background image displaced
1.60 + downwards (or upwards having wrapped around) on the
1.61 + screen. */
1.62 +
1.63 + if (yorigin)
1.64 + copy_display_section(&display_config, screendata,
1.65 + screendata_width, screendata_height,
1.66 + xsource, 0,
1.67 + column_width, yorigin,
1.68 + xdisplay, screendata_height - yorigin,
1.69 + -1, 1);
1.70 }
1.71 }
1.72
