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Fixed Space Invaders buffer update (the left-most pixel of every byte is bit 0, not bit 7 as in PC video adapters)

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This commit is contained in:
Jeff Parsons 2016-05-02 16:19:50 -07:00
commit 3941cf8ff6
3 changed files with 47 additions and 13 deletions
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50
modules/pc8080/lib/video.js
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@ -55,20 +55,21 @@ if (NODE) {
* bufferAddr: the starting address of the frame buffer (eg, 0x2400)
* bufferCols: the width of a single frame buffer row, in pixels (eg, 256)
* bufferRows: the number of frame buffer rows (eg, 224)
* bufferBits: the number of bits per pixel (default is 1 if omitted)
* bufferBits: the number of bits per column (default is 1 if omitted)
* bufferLeft: the bit position of the left-most pixel in a byte (eg, 0)
* interruptRate: normally the same as (or some multiple of) refreshRate (eg, 120)
* refreshRate: how many times updateScreen() should be performed per second (eg, 60)
*
* We record all the above values now, but we defer creation of the frame buffer until our initBus()
* handler is called. At that point, we will also compute the extent of the frame buffer, determine the
* appropriate "cell" size (ie, the number of pixels that updateScreen() will fetch and process at once),
* and allocate our cell cache.
* and then allocate our cell cache.
*
* Why interruptRate in addition to refreshRate? A higher interrupt rate is required for Space Invaders,
* because even though the CRT refreshes at 60Hz, the CRT controller interrupts the CPU *twice* per
* refresh (once after the top half of the screen has been redrawn, and again after the bottom half has
* been redrawn), so we need an interrupt rate of 120Hz. We pass the higher rate on to the CPU, so that
* it will call updateScreen() more frequently, but we limit our screen updates to every *other* call.
* it will call updateScreen() more frequently, but we still limit our screen updates to every *other* call.
*
* TODO: Consider alternatives to screenRotation; it's expedient, but I'm not sure how efficient it is,
* and it might be nice (especially for debugging) if we created our own rotated image buffer which we could
@ -93,6 +94,7 @@ function Video(parmsVideo, canvas, context, textarea, container)
this.cxBuffer = parmsVideo['bufferCols'];
this.cyBuffer = parmsVideo['bufferRows'];
this.nBitsPerPixel = parmsVideo['bufferBits'] || 1;
this.iBitFirstPixel = parmsVideo['bufferLeft'] || 0;
this.interruptRate = parmsVideo['interruptRate'];
this.refreshRate = parmsVideo['refreshRate'] || 60;
@ -233,6 +235,28 @@ Video.prototype.setPixel = function(imageData, x, y, rgb)
* and then update the cell cache to match. Since initCache() sets every cell in the cell cache to an
* invalid value, we're assured that the next call to updateScreen() will redraw the entire (visible) video buffer.
*
* Example
* -------
*
* The initial Space Invaders screen displays an "S" (part of the word "SCORE") at the end of these rows:
*
* 2520 00 42 01 00 00 00 00 00-00 00 00 00 00 00 00 00 .B..............
* 2530 00 00 00 00 00 00 00 00-00 00 00 00 00 00 32 00 ..............2.
* 2540 00 41 01 00 00 00 00 00-00 00 00 00 00 00 00 00 .A..............
* 2550 00 00 00 00 00 00 00 00-00 00 00 00 00 00 49 00 ..............I.
* 2560 00 49 01 00 00 00 00 00-00 00 00 00 00 00 00 00 .I..............
* 2570 00 00 00 00 00 00 00 00-00 00 00 00 00 00 49 00 ..............I.
* 2580 00 59 01 00 00 00 00 00-00 00 00 00 00 00 00 00 .Y..............
* 2590 00 00 00 00 00 00 00 00-00 00 00 00 00 00 49 00 ..............I.
* 25A0 00 66 01 00 00 00 00 00-00 00 00 00 00 00 00 00 .f..............
* 25B0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 26 00 ..............&.
*
* 32 ..11..1. .1..11..
* 49 .1..1..1
* 49 .1..1..1
* 49 .1..1..1
* 26 ..1..11.
*
* @this {Video}
* @param {number} n (where 0 <= n < getRefreshRate() for a normal update, or -1 for a forced update)
*/
@ -266,7 +290,6 @@ Video.prototype.updateScreen = function(n)
var addrLimit = addr + this.sizeBuffer;
var iCell = 0;
var wPixelMask = 0x10000;
var nPixelShift = 1;
var aPixelColors = this.getColors();
@ -280,22 +303,27 @@ Video.prototype.updateScreen = function(n)
xBuffer += this.nPixelsPerCell;
} else {
this.aCellCache[iCell] = data;
var wPixels = (data >> 8) | ((data & 0xff) << 8);
var wMask = wPixelMask, nShift = 16;
var nShift = 0;
var nShiftPixel = this.nBitsPerPixel;
var nMask = (1 << nShiftPixel) - 1;
if (this.iBitFirstPixel) {
nShift = 16 - nShiftPixel;
nShiftPixel = -nShiftPixel;
data = ((data >> 8) | ((data & 0xff) << 8));
}
if (xBuffer < xDirty) xDirty = xBuffer;
for (var iPixel = 0; iPixel < this.nPixelsPerCell; iPixel++) {
var bPixel = (wPixels & (wMask >>= nPixelShift)) >> (nShift -= nPixelShift);
var bPixel = (data >> nShift) & nMask;
this.setPixel(this.imageBuffer, xBuffer++, yBuffer, aPixelColors[bPixel]);
nShift += nShiftPixel;
}
if (xBuffer > xMaxDirty) xMaxDirty = xBuffer;
if (yBuffer < yDirty) yDirty = yBuffer;
if (yBuffer >= yMaxDirty) yMaxDirty = yBuffer + 1;
}
addr += 2;
iCell++;
addr += 2; iCell++;
if (xBuffer >= this.cxBuffer) {
xBuffer = 0;
yBuffer++;
xBuffer = 0; yBuffer++;
if (yBuffer > this.cyBuffer) break;
}
}