mirror of https://github.com/fadden/fdraw.git
Fix code formatting
Was indented two spaces, needed to be four.
This commit is contained in:
Andy McFadden
parent
9193ea7f36
commit
c813bc0acd
102
docs/manual.md
102
docs/manual.md
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@ -538,25 +538,25 @@ fast.
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Circles are computed with Bresenham's algorithm. The idea is to compute
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one octant of the circle with this bit of magic:
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void drawOutline(int cx, int cy, int rad) {
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int x, y, d;
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void drawOutline(int cx, int cy, int rad) {
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int x, y, d;
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d = 1 - rad;
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x = 0;
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y = rad;
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d = 1 - rad;
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x = 0;
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y = rad;
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while (x <= y) {
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plot(cx, cy, x, y);
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while (x <= y) {
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plot(cx, cy, x, y);
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if (d < 0) {
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d = d + (x * 4) + 3;
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} else {
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d = d + ((x - y) * 4) + 5;
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y--;
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if (d < 0) {
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d = d + (x * 4) + 3;
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} else {
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d = d + ((x - y) * 4) + 5;
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y--;
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}
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x++;
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}
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x++;
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}
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}
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Then each X/Y coordinate is plotted eight times:
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@ -607,31 +607,31 @@ make it 11 units wide and 21 units high. To draw that in the middle of
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the screen, we'd set CX=139 and CY=95, then draw lines offset from that
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by +/- 5 in X and +/- 10 in Y:
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HPLOT CX-5,CY-10 TO CX-5,CY+10 : REM LEFT
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HPLOT CX-5,CY-10 TO CX+5,CY-10 : REM TOP
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HPLOT CX+5,CY-10 TO CX+5,CY+10 : REM RIGHT
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HPLOT CX-5,CY+10 TO CX+5,CY+10 : REM BOTTOM
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HPLOT CX-5,CY-10 to CX+5,CY+10 : SLASH
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HPLOT CX+5,CY-10 to CX-5,CY+10 : BACKSLASH
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HPLOT CX-5,CY-10 TO CX-5,CY+10 : REM LEFT
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HPLOT CX-5,CY-10 TO CX+5,CY-10 : REM TOP
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HPLOT CX+5,CY-10 TO CX+5,CY+10 : REM RIGHT
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HPLOT CX-5,CY+10 TO CX+5,CY+10 : REM BOTTOM
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HPLOT CX-5,CY-10 to CX+5,CY+10 : SLASH
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HPLOT CX+5,CY-10 to CX-5,CY+10 : BACKSLASH
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Six lines, each of which needs four coordinates. We'd need 24 bytes
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to store that in an integer array.
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Suppose instead we identified the four vertices, and numbered them:
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#0 CX-5,CY-10
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#1 CX+5,CY-10
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#2 CX-5,CY+10
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#3 CX+5,CY+10
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#0 CX-5,CY-10
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#1 CX+5,CY-10
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#2 CX-5,CY+10
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#3 CX+5,CY+10
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and then created a list of line segments using the vertex indices:
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HPLOT #0 TO #2
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HPLOT #0 to #1
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HPLOT #1 TO #3
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HPLOT #2 TO #3
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HPLOT #0 TO #3
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HPLOT #1 TO #2
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HPLOT #0 TO #2
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HPLOT #0 to #1
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HPLOT #1 TO #3
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HPLOT #2 TO #3
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HPLOT #0 TO #3
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HPLOT #1 TO #2
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This requires (4 * 2) + (6 * 2) = 20 bytes, for a small savings. The real
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value in the approach is that it separates the description of the shape
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@ -750,8 +750,8 @@ The Amperfdraw API is somewhat minimal and could be improved. Taking a
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cue from Beagle Graphics, the rect and circle calls should probably look
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more like:
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&DRAW width,height [AT left,top]
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&COS radius [AT left,top]
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&DRAW width,height [AT left,top]
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&COS radius [AT left,top]
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The "&AT" coordinate, currently only used by &PLOT, should be more
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widely used. Not only is it more convenient, it's also slightly faster,
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@ -821,26 +821,26 @@ line at X=17. There's already a green dot at X=15, which gives us a
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bit pattern of 00000010. (Bits are "backwards", i.e. the bit on the
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right is the pixel on the left.)
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LDY byteoffset X=2
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LDX bitoffset X=3
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LDA bitmask,x A=0x88 (10001000)
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STA <andmask
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LDA oddevencolor,y 4 cyc A=0x2a (00101010)
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EOR (hbasl),y 5 cyc A=0x28 (00101010 ^ 00000010 = 00101000)
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AND <andmask 3 cyc A=0x08 (00101000 & 10001000 = 00001000)
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EOR (hbasl),y 5 cyc A=0x0a (00001000 ^ 00000010 = 00001010)
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STA (hbasl),y 6 cyc
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LDY byteoffset X=2
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LDX bitoffset X=3
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LDA bitmask,x A=0x88 (10001000)
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STA <andmask
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LDA oddevencolor,y 4 cyc A=0x2a (00101010)
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EOR (hbasl),y 5 cyc A=0x28 (00101010 ^ 00000010 = 00101000)
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AND <andmask 3 cyc A=0x08 (00101000 & 10001000 = 00001000)
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EOR (hbasl),y 5 cyc A=0x0a (00001000 ^ 00000010 = 00001010)
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STA (hbasl),y 6 cyc
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As a second example, here's how we plot a black1 (hcolor=4) point at X=6
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when there's a purple point (hcolor=2) at X=0 (00000001).
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LDA bitmask,x A=0xc0 (11000000)
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STA <andmask
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LDA oddevencolor,y 4 cyc A=0x80 (10000000)
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EOR (hbasl),y 5 cyc A=0x81 (10000000 ^ 10000001 = 00000001)
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AND <andmask 3 cyc A=0x81 (00000001 & 11000000 = 00000000)
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EOR (hbasl),y 5 cyc A=0x81 (00000000 ^ 10000001 = 10000001)
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STA (hbasl),y 6 cyc
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LDA bitmask,x A=0xc0 (11000000)
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STA <andmask
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LDA oddevencolor,y 4 cyc A=0x80 (10000000)
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EOR (hbasl),y 5 cyc A=0x81 (10000000 ^ 10000001 = 00000001)
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AND <andmask 3 cyc A=0x81 (00000001 & 11000000 = 00000000)
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EOR (hbasl),y 5 cyc A=0x81 (00000000 ^ 10000001 = 10000001)
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STA (hbasl),y 6 cyc
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Note the purple pixel is still set, but now the high bit is as well,
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changing it to blue.
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@ -876,9 +876,9 @@ For 3D games like Stellar 7 or Elite, which essentially draw thin
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monochromatic lines, we can drop the color mask and just set the bit on
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the screen. Plotting a pixel is then simply:
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LDA (hbasl),y 5 cyc
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ORA <bitmask 3 cyc
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STA (hbasl),y 6 cyc
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LDA (hbasl),y 5 cyc
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ORA <bitmask 3 cyc
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STA (hbasl),y 6 cyc
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This cuts the cycle count from 23 to 14. It's also not necessary to
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worry about the high bit, which can save a few cycles when shifting
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