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https://github.com/irmen/prog8.git
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250 lines
7.3 KiB
Lua
250 lines
7.3 KiB
Lua
%target c64
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%import textio
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; bitmap pixel graphics module for the C64
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; only black/white monchrome 320x200 for now
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; assumes bitmap screen memory is $2000-$3fff
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graphics {
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const uword BITMAP_ADDRESS = $2000
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const uword WIDTH = 320
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const ubyte HEIGHT = 200
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sub enable_bitmap_mode() {
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; enable bitmap screen, erase it and set colors to black/white.
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c64.SCROLY = %00111011
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c64.SCROLX = %00001000
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c64.VMCSB = (c64.VMCSB & %11110000) | %00001000 ; $2000-$3fff
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clear_screen(1, 0)
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}
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sub disable_bitmap_mode() {
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; enables text mode, erase the text screen, color white
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c64.SCROLY = %00011011
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c64.SCROLX = %00001000
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c64.VMCSB = (c64.VMCSB & %11110000) | %00000100 ; $1000-$2fff
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txt.fill_screen(' ', 1)
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}
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sub clear_screen(ubyte pixelcolor, ubyte bgcolor) {
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memset(BITMAP_ADDRESS, 320*200/8, 0)
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txt.fill_screen(pixelcolor << 4 | bgcolor, 0)
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}
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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 rewrite this in optimized assembly
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if y1>y2 {
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; make sure dy is always positive to avoid 8 instead of just 4 special cases
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swap(x1, x2)
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swap(y1, y2)
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}
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word @zp d = 0
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ubyte positive_ix = true
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word @zp dx = x2-x1 as word
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word @zp dy = y2-y1
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if dx < 0 {
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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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internal_plotx = x1
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if dx >= dy {
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if positive_ix {
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repeat {
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internal_plot(y1)
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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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if d > dx {
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y1++
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d -= dx
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}
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}
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} else {
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repeat {
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internal_plot(y1)
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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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if d > dx {
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y1++
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d -= dx
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}
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}
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}
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}
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else {
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if positive_ix {
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repeat {
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internal_plot(y1)
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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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if d > dy {
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internal_plotx++
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d -= dy
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}
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}
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} else {
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repeat {
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internal_plot(y1)
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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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if d > dy {
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internal_plotx--
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d -= dy
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}
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}
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}
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}
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}
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sub circle(uword xcenter, ubyte ycenter, ubyte radius) {
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; Midpoint algorithm
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ubyte @zp ploty
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ubyte @zp xx = radius
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ubyte @zp yy = 0
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byte @zp decisionOver2 = 1-xx as byte
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while xx>=yy {
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internal_plotx = xcenter + xx
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ploty = ycenter + yy
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internal_plot(ploty)
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internal_plotx = xcenter - xx
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internal_plot(ploty)
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internal_plotx = xcenter + xx
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ploty = ycenter - yy
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internal_plot(ploty)
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internal_plotx = xcenter - xx
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internal_plot(ploty)
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internal_plotx = xcenter + yy
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ploty = ycenter + xx
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internal_plot(ploty)
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internal_plotx = xcenter - yy
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internal_plot(ploty)
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internal_plotx = xcenter + yy
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ploty = ycenter - xx
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internal_plot(ploty)
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internal_plotx = xcenter - yy
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internal_plot(ploty)
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yy++
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if decisionOver2<=0
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decisionOver2 += 2*yy+1
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else {
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xx--
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decisionOver2 += 2*(yy-xx)+1
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}
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}
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}
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sub disc(uword xcenter, ubyte ycenter, ubyte radius) {
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; Midpoint algorithm, filled
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ubyte xx = radius
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ubyte yy = 0
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byte decisionOver2 = 1-xx as byte
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while xx>=yy {
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ubyte ycenter_plus_yy = ycenter + yy
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ubyte ycenter_min_yy = ycenter - yy
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ubyte ycenter_plus_xx = ycenter + xx
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ubyte ycenter_min_xx = ycenter - xx
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internal_plotx = xcenter-xx
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repeat xx*2+1 {
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internal_plot(ycenter_plus_yy)
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internal_plot(ycenter_min_yy)
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internal_plotx++
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}
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internal_plotx = xcenter-yy
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repeat yy*2+1 {
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internal_plot(ycenter_plus_xx)
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internal_plot(ycenter_min_xx)
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internal_plotx++
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}
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yy++
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if decisionOver2<=0
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decisionOver2 += 2*yy+1
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else {
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xx--
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decisionOver2 += 2*(yy-xx)+1
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}
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}
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}
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; here is the non-asm code for the plot routine below:
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; sub plot_nonasm(uword px, ubyte py) {
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; ubyte[] ormask = [128, 64, 32, 16, 8, 4, 2, 1]
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; uword addr = BITMAP_ADDRESS + 320*(py>>3) + (py & 7) + (px & %0000000111111000)
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; @(addr) |= ormask[lsb(px) & 7]
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; }
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asmsub plot(uword plotx @XY, ubyte ploty @A) clobbers (A, X, Y) {
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%asm {{
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stx internal_plotx
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sty internal_plotx+1
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jmp internal_plot
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}}
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}
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; for efficiency of internal algorithms here is the internal plot routine
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; that takes the plotx coordinate in a separate variable instead of the XY register pair:
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uword internal_plotx ; 0..319 ; separate 'parameter' for internal_plot()
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asmsub internal_plot(ubyte ploty @A) clobbers (A, X, Y) { ; internal_plotx is 16 bits 0 to 319... doesn't fit in a register
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%asm {{
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tay
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lda internal_plotx+1
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sta P8ZP_SCRATCH_W2+1
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lsr a ; 0
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sta P8ZP_SCRATCH_W2
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lda internal_plotx
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pha
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and #7
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tax
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lda _y_lookup_lo,y
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W2
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lda _y_lookup_hi,y
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adc P8ZP_SCRATCH_W2+1
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sta P8ZP_SCRATCH_W2+1
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pla ; internal_plotx
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and #%11111000
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tay
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lda (P8ZP_SCRATCH_W2),y
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ora _ormask,x
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sta (P8ZP_SCRATCH_W2),y
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rts
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_ormask .byte 128, 64, 32, 16, 8, 4, 2, 1
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; note: this can be even faster if we also have a 256 byte x-lookup table, but hey.
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; see http://codebase64.org/doku.php?id=base:various_techniques_to_calculate_adresses_fast_common_screen_formats_for_pixel_graphics
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; the y lookup tables encodes this formula: BITMAP_ADDRESS + 320*(py>>3) + (py & 7) (y from 0..199)
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; We use the 64tass syntax for range expressions to calculate this table on assembly time.
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_plot_y_values := $2000 + 320*(range(200)>>3) + (range(200) & 7)
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_y_lookup_lo .byte <_plot_y_values
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_y_lookup_hi .byte >_plot_y_values
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}}
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}
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}
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