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vic20: fix the text window geometry
The VIC-I draws a fixed 22x23 character window, centered in the picture. The emulator used the VIC-II's display window registers, so the window was placed at a garbage offset: the first character column was clipped in half and the whole picture was shifted 24 pixels to the right to hide it. - the new emulator core (chips) centers the window and takes its vertical position from the ROM, so NTSC and PAL ROMs both work - the 24 pixel video shift is gone - the platform loads res/vic20/vic20.bios (a real ROM set) when it is available, and falls back to the stub BIOS otherwise - a regression test checks the geometry of the rendered frame
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@@ -2,6 +2,10 @@
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## [Unreleased]
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### Emulators
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- **VIC-20**: the text window is drawn correctly now. The VIC-I emulated the VIC-II's display window registers, so the 22 column window was placed at a garbage offset: the first character column was clipped in half and the screen was shifted 24 pixels to the right. The VIC-I window is fixed at 22x23 characters and centered in the picture; its vertical position still comes from the ROM (the "upper border" register), so NTSC and PAL ROMs both work.
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### Editor and UI
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- The IDE now works in Firefox: a synchronous XHR with a `responseType` hangs in Firefox when the response is 1MB or more, so the build worker hung forever on platforms with a big toolchain package (Game Boy, Atari 8-bit, Apple II, ...). The worker now fetches those packages as ArrayBuffers. A worker that dies no longer leaves the IDE spinning: the error is shown and the build stops.
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@@ -15,7 +15,9 @@ export class VIC20_WASMMachine extends BaseWASMMachine implements Machine, Probe
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numTotalScanlines = 312;
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cpuCyclesPerLine = 71;
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videoOffsetBytes = -24 * 4;
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// the VIC-I draws its 22x23 character window centered in the frame,
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// so no video offset is needed
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videoOffsetBytes = 0;
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prgstart : number;
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joymask0 = 0;
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@@ -27,6 +29,22 @@ export class VIC20_WASMMachine extends BaseWASMMachine implements Machine, Probe
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super.loadBIOS(srcArray);
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}
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async fetchBIOS() {
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// use the real VIC-20 ROM set (BASIC, character ROM and KERNAL) if it is
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// available, otherwise fall back to a tiny stub BIOS that only knows how
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// to start an autostart cartridge
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try {
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const resp = await fetch('res/vic20/vic20.bios');
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if (resp.status == 200) {
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const bios = new Uint8Array(await resp.arrayBuffer());
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if (bios.length == 0x5000) {
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this.allocateBIOS(bios);
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this.loadBIOS(bios);
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return;
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}
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}
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} catch (e) {
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// no ROM set available, use the stub BIOS below
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}
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let bios = new Uint8Array(20480);
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bios.set(DEFAULT_BIOS, bios.length - DEFAULT_BIOS.length);
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this.allocateBIOS(bios);
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@@ -0,0 +1,95 @@
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var assert = require('assert');
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var { loadPlatform } = require('../../gen/tools/emutarget.js');
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/*
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A tiny cartridge that programs the VIC-I and draws two characters, so
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that the text window can be checked.
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The cartridge file has a 2 byte load address, then the cold and warm
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start vectors, then the "A0CBM" signature; the code is loaded at $A009:
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$A009 A9 1B LDA #$1B ; bg color white, border color cyan
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$A00B 8D 0F 90 STA $900F
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$A00D A9 19 LDA #$19 ; upper border = raster line 25
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$A00F 8D 01 90 STA $9001
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$A011 A9 F0 LDA #$F0 ; screen pointer A13..A10
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$A013 8D 05 90 STA $9005
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$A015 A9 96 LDA #$96 ; screen pointer A9
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$A017 8D 02 90 STA $9002
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$A019 A9 00 LDA #$00 ; clear the screen page
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$A01B A2 00 LDX #$00
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$A01D 9D 00 1E STA $1E00,X
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$A020 9D 00 1F STA $1F00,X
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$A023 E8 INX
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$A024 D0 F7 BNE $A01D
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$A026 A9 06 LDA #$06 ; clear the color RAM, blue
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$A028 A2 00 LDX #$00
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$A02A 9D 00 96 STA $9600,X
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$A02D E8 INX
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$A02E E0 28 CPX #$28
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$A030 D0 F8 BNE $A02A
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$A032 A9 48 LDA #'H'
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$A034 8D 00 1E STA $1E00
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$A037 A9 49 LDA #'I'
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$A039 8D 01 1E STA $1E01
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$A03C 4C 40 A0 JMP $A040
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$A03F 00
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$A040 4C 40 A0 JMP $A040
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*/
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var CART = [
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0x00, 0xA0, 0x09, 0xA0, 0x09, 0xA0, 0x41, 0x30, 0xC3, 0xC2, 0xCD, 0xA9,
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0x1B, 0x8D, 0x0F, 0x90, 0xA9, 0x19, 0x8D, 0x01, 0x90, 0xA9, 0xF0, 0x8D,
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0x05, 0x90, 0xA9, 0x96, 0x8D, 0x02, 0x90, 0xA9, 0x00, 0xA2, 0x00, 0x9D,
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0x00, 0x1E, 0x9D, 0x00, 0x1F, 0xE8, 0xD0, 0xF7, 0xA9, 0x06, 0xA2, 0x00,
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0x9D, 0x00, 0x96, 0xE8, 0xE0, 0x28, 0xD0, 0xF8, 0xA9, 0x48, 0x8D, 0x00,
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0x1E, 0xA9, 0x49, 0x8D, 0x01, 0x1E, 0x4C, 0x40, 0xA0,
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];
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var CYAN = 0xFFFFF04D;
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describe('VIC-20 video', function () {
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it('should draw the 22 column text window centered in the frame', async function () {
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this.timeout(60000);
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var target = await loadPlatform('vic20');
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await target.start();
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var video = target.getVideo();
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assert.equal(video.width, 232);
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assert.equal(video.height, 272);
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// load the cartridge that programs the VIC
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await target.loadROM(new Uint8Array(CART), 'cart.bin');
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// run until the cartridge has set up the screen (with a real KERNAL
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// this takes a moment, with the stub BIOS it is immediate)
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var color = function () { return -1; };
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for (var i = 0; i < 300; i++) {
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target.advanceFrame();
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video = target.getVideo();
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var px = video.pixels;
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color = function (x, y) { return px[y * video.width + x]; };
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if (color(0, 100) == CYAN) break;
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}
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assert.equal(color(0, 100), CYAN, 'the cartridge screen did not appear');
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// the cartridge sets the colors before the window position, so let
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// a few more frames pass before the picture is checked
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for (var i = 0; i < 5; i++) {
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target.advanceFrame();
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}
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video = target.getVideo();
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var px = video.pixels;
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color = function (x, y) { return px[y * video.width + x]; };
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// the text window is 22 columns (176 pixels) wide and centered, so
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// there are 28 pixels of border color on either side. The pixels
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// inside the window are the background color or a character, but
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// never the border color.
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assert.equal(color(0, 100), CYAN, 'left border');
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assert.equal(color(27, 100), CYAN, 'left border');
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assert.notEqual(color(28, 100), CYAN, 'first text column');
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assert.notEqual(color(203, 100), CYAN, 'last text column');
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assert.equal(color(204, 100), CYAN, 'right border');
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assert.equal(color(231, 100), CYAN, 'right border');
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// the window is 23 rows (184 lines) tall, starting at raster line 25
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assert.equal(color(100, 25), CYAN, 'above the text window');
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assert.notEqual(color(100, 26), CYAN, 'first text row');
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assert.notEqual(color(100, 209), CYAN, 'last text row');
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assert.equal(color(100, 210), CYAN, 'below the text window');
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});
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});
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