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110 lines
3.4 KiB
C
110 lines
3.4 KiB
C
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/*
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* apple2.text.c
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*
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* This code sits as a kind of wrapper over the bitmap fonts that the
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* Apple II uses. Neither the system nor inverted fonts are exactly
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* composed in the type of character set that Apple expects; they
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* implement the glpyhs we need in order to make such. You can have
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* inversed characters in the primary character set, for one; in the
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* alternate character set, you can have MouseText glyphs, yet they are
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* implemented as part of both fonts.
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*/
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#include "apple2.text.h"
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void
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apple2_text_draw(apple2 *mach, size_t addr)
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{
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int err;
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vm_8bit ch;
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vm_area dest;
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vm_bitfont *font;
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// If we're updating a page 2 address and we're not in some kind of
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// double resolution mode, then we shouldn't actually render the
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// thing.
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if (addr > 0x07FF && !apple2_is_double_video(mach)) {
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return;
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}
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// Default
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font = mach->sysfont;
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err = apple2_text_area(&dest, font, addr);
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if (err != OK) {
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return;
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}
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// What are we working with?
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ch = mos6502_get(mach->cpu, addr);
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// We treat special characters as spaces for display purposes.
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if (ch < 0x20) {
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vm_bitfont_render(font, mach->screen, &dest, ' ');
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return;
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}
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// Blank out the space on the screen, then show the character
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vm_bitfont_render(font, mach->screen, &dest, ' ');
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vm_bitfont_render(font, mach->screen, &dest, ch);
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}
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int
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apple2_text_area(vm_area *area, vm_bitfont *font, size_t addr)
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{
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vm_8bit lsb;
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int page_base;
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// The text display buffers are located at "Page 1" and "Page 2",
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// which are at byte 1024-2047 (0x0400-0x07FF) and byte 2048-3071
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// (0x0800-0x0BFF) respectively. If the given address is not in
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// those (contiguous) ranges, then let's bail.
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if (addr < 0x0400 || addr > 0x0BFF) {
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return 0;
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}
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// In a given page for 40-column mode, you get 960 grid parts that
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// you may use. In 80-column mode, it's more like 1920 grid parts
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// (40x24 = 960, 80x24 = 1920). The way we look at this is the
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// address indicates the place on the grid where text should go. We
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// don't care how it got there. Let's figure out that position
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// on-screen.
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lsb = addr & 0xff; // column
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// Regardless of which page we're rendering into, we can only use 40
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// cells on the grid (that is, 0-39 from whatever value the msb is).
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// It's possible to have an lsb greater than that, but if so, it's
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// not anything we can render to the screen.
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if (lsb > 0x39) {
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return 0;
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}
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if ((addr & 0xff80) % 128 != 0) {
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return 0;
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}
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// By default, we assume we're in text page 1. If the address ends
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// up being greater than 0x07FF, then we must be in page 2.
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page_base = 0x0400;
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if (addr > 0x07FF) {
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page_base = 0x0800;
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}
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// The absolute column position will be the font width times the
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// lsb.
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area->xoff = lsb * font->width;
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// The absolute row position will be the font height times the msb
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// minus the page base (because the height is the same regardless of
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// what page we're in). So if we're msb $0400, then we're starting
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// on pixel row 0; but if we're msb $0480, then we are starting on
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// pixel row 8 (where the font height is 8); etc.
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area->yoff = ((addr & 0xff80) - page_base) * font->height;
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// Our width and height must be that of the font.
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area->width = font->width;
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area->height = font->height;
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return OK;
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}
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