jsbasic/hires.js

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//
// High Resolution Graphics (HiRes) Emulation
//
// This variation does not rely on a canvas element with the same dimensions
// as the pixel buffer; instead, it paints pixels on the canvas using rectangles.
// This works even if the underlying canvas implementation does not support
// scaling (e.g. fallbacks for IE using VML or Flash)
// Usage:
//
// var hires = new LoRes( element, width, height )
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// hires.clear( [color_index] )
// hires.setColor( color_index )
// hires.plot( x, y )
// hires.plot_to( x, x )
// hires.getPixel( x, x ) // for "HSCRN"
// hires.show( bool )
// { width: w, height: h } = hires.getScreenSize()
function HiRes(element, width, height) {
var COLORS, // Apple II to HTML color table
last_x = 0,
last_y = 0,
pixels = [],
color = 0,
context = element.getContext("2d");
pixels.length = width * height;
// Colors c/o USENET:
// Date: Wed, 05 Sep 2007 01:04:20 +0200
// From: Linards Ticmanis <ticmanis@gmx.de>
// Newsgroups: comp.sys.apple2
// Subject: Re: Double hires mode color artifacts
// Message-ID: <46dde477$0$4527$9b4e6d93@newsspool3.arcor-online.net>
COLORS = [
'#000000', // Black 1
'#2fbc1a', // Green
'#d043e5', // Violet
'#ffffff', // White 1
'#000000', // Black 2
'#d06a1a', // Orange
'#2f95e5', // Medium Blue
'#ffffff' // White 2
];
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this.clear = function(opt_color) {
var i;
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context.clearRect(0, 0, element.width, element.height);
pixels = [];
pixels.length = width * height;
if (arguments.length >= 1) {
context.fillStyle = COLORS[opt_color];
context.fillRect(0, 0, element.width, element.height);
for (i = 0; i < pixels.length; i += 1) {
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pixels[i] = opt_color;
}
}
};
this.setColor = function(newColor) {
color = Math.floor(newColor) % COLORS.length;
};
function drawPixel(x, y) {
var sx = element.width / width,
sy = element.height / height;
context.fillRect(x * sx, y * sy, sx, sy);
pixels[x + y * width] = color;
}
this.plot = function(x, y) {
context.fillStyle = COLORS[color];
drawPixel(x, y);
last_x = x;
last_y = y;
};
this.plot_to = function(x, y) {
var x0 = last_x, y0 = last_y, x1 = x, y1 = y,
dx = Math.abs(x1 - x0),
dy = Math.abs(y1 - y0),
sx = (x0 < x1) ? 1 : -1,
sy = (y0 < y1) ? 1 : -1,
err = dx - dy,
e2;
while (true) {
this.plot(x0, y0);
if (x0 === x1 && y0 === y1) { return; }
e2 = 2 * err;
if (e2 > -dy) {
err -= dy;
x0 += sx;
}
if (e2 < dx) {
err += dx;
y0 += sy;
}
}
last_x = x;
last_y = y;
};
this.getPixel = function(x, y) {
return pixels[y * width + x] >>> 0;
};
this.getScreenSize = function() {
return { width: width, height: height };
};
this.show = function(state) {
element.style.visibility = state ? "visible" : "hidden";
};
}