1 files changed, 94 insertions, 0 deletions
diff --git a/render.s b/render.s
new file mode 100644
index 0000000..867003e
--- /dev/null
+++ b/render.s
@@ -0,0 +1,94 @@
+;;; Subroutine: render
+;;; Convert 1px per byte array at pixarray to packed 8px/byte at screen.
+; pixarray is 170x170. screen is 256x170 (TODO: fix display list).
+; each screen line is: 43 blank px, 170 graphics px, 43 blank.
+ screenbyte = FR0
+ colcount = FR0+1
+
+render:
+ lda #<screen
+ sta screenptr
+ lda #>screen
+ sta screenptr+1
+ lda #<pixarray
+ sta pixptr
+ lda #>pixarray
+ sta pixptr+1
+
+ ldx #0
+rline:
+ lda #0
+ sta colcount
+ sta screenbyte
+
+; ; clear 40px on left
+; ldy #4
+;lclr:
+; sta (screenptr),y
+; dey
+; bpl lclr
+;
+; ; clear 40px on right
+; ldy #$1b
+;rclr:
+; sta (screenptr),y
+; iny
+; cpy #$20
+; bne rclr
+
+; clear whole line. this is why pixarray is offset from screen by
+; one screen line.
+ ldy #$1f
+rclr:
+ sta (screenptr),y
+ dey
+ bpl rclr
+
+ ; first pixels start at column 40, plus...
+ lda #5
+ sta screenbyte
+ lda #$10 ; ...mask starts out 0001000, 3 more blank px on left
+ sta pixmask
+
+rpix:
+ ldy colcount ; ranges 0 to 169
+ lda (pixptr),y
+ beq notset     ; 0 = not set, non-zero = set
+ ; if we found a set pixel, set it in the bitmap
+ ldy screenbyte
+ lda (screenptr),y
+ ora pixmask
+ sta (screenptr),y
+notset:
+ ; pixmask >>= 1; if(pixmask == 0) { pixmask = 0x80; screenbyte++; }
+ lsr pixmask
+ bne pmok
+ ;ror pixmask
+ lda #$80
+ sta pixmask
+ inc screenbyte
+pmok:
+ inc colcount
+ lda colcount
+ cmp #$aa
+ bne rpix
+ ; pixptr += 0xaa;
+ clc
+ adc pixptr
+ sta pixptr
+ lda pixptr+1
+ adc #0
+ sta pixptr+1
+ ; screenptr += 0x20;
+ clc
+ lda screenptr
+ adc #$20
+ sta screenptr
+ lda screenptr+1
+ adc #0
+ sta screenptr+1
+ inx
+ cpx #$aa ; hit last line yet?
+ bne rline ; if not, go render next line.
+
+ rts