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Fix an offset bug

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This commit is contained in:
Lucas Scharenbroich 2021-07-27 09:45:28 -05:00
parent 87e46d95f5
commit 39e3fa9364
1 changed files with 4 additions and 4 deletions
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8
tools/mkrot.js
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@ -1,13 +1,13 @@
/**
* Generated data tables for BG1 rotation
*
* The tickiest issue to address is that, when calculating the rotation indices, at
* The trickiest issue to address is that, when calculating the rotation indices, at
* a 45 degree angle, the mapped address for a fixed rectangle can be outside of the
* pixel buffer. To fix this we make a compromise.
*
* To keep speed, image data is drawn one word at a time, so the effective width of the
* rotation is 82 units wide. Since each work contains 4 pixels, we will only rotate
* a quarter of the vertical image -- an effective 52 units -- and display the save offset
* a quarter of the vertical image -- an effective 52 units -- and display the same offset
* for four consecutive lines.
*
* Further, the image data will be the center of the BG1 buffer, so the middle 52 lines.
@ -16,7 +16,7 @@
* sqrt(2) (~40%) -- or 32 words horizontally and 21 lines vertically. There is extra
* data vertically to fill this and, since the BG1 buffer is stored with a stride of
* 256 bytes (128 words) there are an extra 46 words of empty space that can be zeroed
* out or filled with content to improve the retation visuals.
* out or filled with content to improve the rotation visuals.
*/
const fs = require('fs').promises;
const process = require('process');
@ -41,7 +41,7 @@ console.log(`; The BG1 buffer lives at [${toHex(BUFFER_START)}, ${toHex(BUFFER_E
// extends down to line
const TEXTURE_START = BUFFER_STRIDE * (BUFFER_HEIGHT - TEXTURE_HEIGHT) / 2;
const TEXTURE_END = BUFFER_STRIDE * (BUFFER_HEIGHT + TEXTURE_HEIGHT) / 2;
const TEXTURE_CENTER = TEXTURE_START + Math.floor(TEXTURE_HEIGHT / 2) * BUFFER_STRIDE + Math.floor(BUFFER_WIDTH / 2);
const TEXTURE_CENTER = BUFFER_START + TEXTURE_START + Math.floor(TEXTURE_HEIGHT / 2) * BUFFER_STRIDE + Math.floor(BUFFER_WIDTH / 2);
console.log(`; The texture is this range of the BG1 buffer [${toHex(TEXTURE_START)}, ${toHex(TEXTURE_END)}]`);