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Fixed a bug introduced by wrongly assuming that I could reverse some logic in part6
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2 changed files with 17 additions and 15 deletions
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@ -20,14 +20,14 @@ void drawChar(unsigned char ch, int x, int y, unsigned char attr, int zoom)
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{
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unsigned char *glyph = (unsigned char *)&font + (ch < FONT_NUMGLYPHS ? ch : 0) * FONT_BPG;
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for (int i=0;i<(FONT_HEIGHT*zoom);i++) {
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for (int i=1;i<=(FONT_HEIGHT*zoom);i++) {
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for (int j=0;j<(FONT_WIDTH*zoom);j++) {
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unsigned char mask = 1 << (j/zoom);
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unsigned char col = (*glyph & mask) ? attr & 0x0f : (attr & 0xf0) >> 4;
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drawPixel(x+j, y+i, col);
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}
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glyph += (i%zoom) ? FONT_BPL : 0;
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glyph += (i%zoom) ? 0 : FONT_BPL;
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}
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}
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```
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@ -70,21 +70,23 @@ j=7 : (j / zoom) = 7 j=7 : (j / zoom) = 3
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... ...
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```
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So, that sorts out our horizontal zoom. To achieve the vertical zoom, it's a similar solution. Instead of advancing our glyph pointer by the number of bytes per line on each iteration, we do it one in every `zoom` iterations by making use of the **modulo** operator (I think of this as "remainder after division"). If `i` divided by `zoom` has a non-zero remainder then we advance our glyph pointer, otherwise we leave it where it is!
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So, that sorts out our horizontal zoom. To achieve the vertical zoom, it's a similar solution. Instead of advancing our glyph pointer by the number of bytes per line on each iteration, we do it one in every `zoom` iterations by making use of the **modulo** operator (I think of this as "remainder after division"). If `i` divided by `zoom` has no remainder then we advance our glyph pointer, otherwise we leave it where it is!
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```c
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zoom=2
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i=0 : (i % zoom) = 0
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i=1 : (i % zoom) = 1 -> advance the pointer
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i=2 : (i % zoom) = 0
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i=3 : (i % zoom) = 1 -> advance the pointer
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i=4 : (i % zoom) = 0
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i=5 : (i % zoom) = 1 -> advance the pointer
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i=6 : (i % zoom) = 0
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i=7 : (i % zoom) = 1 -> advance the pointer
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i=1 : (i % zoom) = 1
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i=2 : (i % zoom) = 0 -> advance the pointer
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i=3 : (i % zoom) = 1
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i=4 : (i % zoom) = 0 -> advance the pointer
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i=5 : (i % zoom) = 1
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i=6 : (i % zoom) = 0 -> advance the pointer
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i=7 : (i % zoom) = 1
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i=8 : (i % zoom) = 0 -> advance the pointer
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...
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```
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By all means make these changes to _fb.c_ in your part5-framebuffer code and exercise them properly in _kernel.c_ to check that they work. Don't forget to update the function definition in _fb.h_ to include the `zoom` parameter too.
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Perhaps you can see why we changed our loop to count from 1 rather than 0?
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It is now trivial to modify `drawString` to take a `zoom` parameter and pass it through, so I won't document the changes here.
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If you want, you can now make these changes to _fb.c_ in your part5-framebuffer code and exercise them properly in _kernel.c_ to check that they work. Don't forget to update the function definition in _fb.h_ to include the `zoom` parameter too.
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It is also now trivial to modify `drawString` to take a `zoom` parameter and pass it through, so I won't document the changes here.
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@ -144,14 +144,14 @@ void drawChar(unsigned char ch, int x, int y, unsigned char attr, int zoom)
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{
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unsigned char *glyph = (unsigned char *)&font + (ch < FONT_NUMGLYPHS ? ch : 0) * FONT_BPG;
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for (int i=0;i<(FONT_HEIGHT*zoom);i++) {
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for (int i=1;i<=(FONT_HEIGHT*zoom);i++) {
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for (int j=0;j<(FONT_WIDTH*zoom);j++) {
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unsigned char mask = 1 << (j/zoom);
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unsigned char col = (*glyph & mask) ? attr & 0x0f : (attr & 0xf0) >> 4;
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drawPixel(x+j, y+i, col);
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}
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glyph += (i%zoom) ? FONT_BPL : 0;
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glyph += (i%zoom) ? 0 : FONT_BPL;
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}
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}
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