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fix c64 bresenham line inaccuracy
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62ec77e148
commit
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@ -34,7 +34,6 @@ graphics {
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sub line(uword @zp x1, ubyte @zp y1, uword @zp x2, ubyte @zp y2) {
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; Bresenham algorithm.
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; This code special-cases various quadrant loops to allow simple ++ and -- operations.
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; TODO there are some slight errors at the first/last pixels in certain slopes...??
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if y1>y2 {
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; make sure dy is always positive to have only 4 instead of 8 special cases
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swap(x1, x2)
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@ -62,8 +61,8 @@ graphics {
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dx = -dx
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positive_ix = false
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}
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dx *= 2
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dy *= 2
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word @zp dx2 = dx*2
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word @zp dy2 = dy*2
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internal_plotx = x1
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if dx >= dy {
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@ -73,10 +72,10 @@ graphics {
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if internal_plotx==x2
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return
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internal_plotx++
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d += dy
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d += dy2
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if d > dx {
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y1++
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d -= dx
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d -= dx2
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}
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}
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} else {
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@ -85,10 +84,10 @@ graphics {
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if internal_plotx==x2
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return
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internal_plotx--
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d += dy
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d += dy2
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if d > dx {
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y1++
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d -= dx
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d -= dx2
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}
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}
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}
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@ -100,10 +99,10 @@ graphics {
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if y1 == y2
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return
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y1++
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d += dx
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d += dx2
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if d > dy {
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internal_plotx++
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d -= dy
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d -= dy2
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}
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}
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} else {
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@ -112,10 +111,10 @@ graphics {
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if y1 == y2
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return
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y1++
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d += dx
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d += dx2
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if d > dy {
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internal_plotx--
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d -= dy
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d -= dy2
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}
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}
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}
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@ -1,39 +1,32 @@
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%import textio
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%import graphics
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%import floats
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%import test_stack
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%zeropage dontuse
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main {
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sub start() {
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graphics.enable_bitmap_mode()
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uword xx
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float fl
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float fltotal=0.0
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ubyte ub = 22
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ubyte yy
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ub = 22
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fl = ub as float
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floats.print_f(fl)
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txt.nl()
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ub = 255
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fl = ub as float
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floats.print_f(fl)
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txt.nl()
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xx = 123
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fl = xx as float
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floats.print_f(fl)
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txt.nl()
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xx = 55555
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fl = xx as float
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floats.print_f(fl)
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txt.nl()
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graphics.line(150,50,150,50)
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fltotal=0.0
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for xx in 1 to 255 {
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fl = xx as float
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fltotal = fl * fl
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for yy in 0 to 199-60 step 16 {
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for xx in 0 to 319-50 step 16 {
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graphics.line(30+xx, 10+yy, 50+xx, 30+yy)
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graphics.line(49+xx, 30+yy, 10+xx, 30+yy)
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graphics.line(11+xx, 29+yy, 29+xx, 11+yy)
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; triangle 2, counter-clockwise
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graphics.line(30+xx, 40+yy, 10+xx, 60+yy)
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graphics.line(11+xx, 60+yy, 50+xx, 60+yy)
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graphics.line(49+xx, 59+yy, 31+xx,41+yy)
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}
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}
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test_stack.test()
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repeat {
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}
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}
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}
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