optimize horzontal_line drawing

compiler/res/prog8lib/c64/graphics.p8

@@ -34,7 +34,6 @@ graphics {
     sub line(uword @zp x1, ubyte @zp y1, uword @zp x2, ubyte @zp y2) {
         ; Bresenham algorithm.
         ; This code special-cases various quadrant loops to allow simple ++ and -- operations.
-        ; TODO rewrite this in optimized assembly
         if y1>y2 {
             ; make sure dy is always positive to have only 4 instead of 8 special cases
             swap(x1, x2)
@@ -54,6 +53,8 @@ graphics {
             return
         }
 
+        ; TODO rewrite the rest in optimized assembly
+
         word @zp d = 0
         ubyte positive_ix = true
         if dx < 0 {
@@ -143,14 +144,82 @@ graphics {
     }
 
     sub horizontal_line(uword x, ubyte y, uword length) {
-        if not length
+        if length<8 {
+            internal_plotx=x
+            repeat lsb(length) {
+                internal_plot(y)
+                internal_plotx++
+            }
             return
+        }
 
-        ; TODO optimized drawing 8 pixels at a time (+edges) should use  get_y_lookup(y) in this
-        internal_plotx = x
-        repeat length {
-            internal_plot(y)
-            internal_plotx++
+        ubyte separate_pixels = lsb(x) & 7
+        uword addr = get_y_lookup(y) + (x&$fff8)
+
+        if separate_pixels {
+            %asm {{
+                lda  addr
+                sta  P8ZP_SCRATCH_W1
+                lda  addr+1
+                sta  P8ZP_SCRATCH_W1+1
+                ldy  separate_pixels
+                lda  _filled_right,y
+                eor  #255
+                ldy  #0
+                ora  (P8ZP_SCRATCH_W1),y
+                sta  (P8ZP_SCRATCH_W1),y
+            }}
+            addr += 8
+            length += separate_pixels
+            length -= 8
+        }
+
+        if length {
+            %asm {{
+                lda  length
+                and  #7
+                sta  separate_pixels
+                stx  P8ZP_SCRATCH_REG
+                lsr  length+1
+                ror  length
+                lsr  length+1
+                ror  length
+                lsr  length+1
+                ror  length
+                lda  addr
+                sta  _modified+1
+                lda  addr+1
+                sta  _modified+2
+                lda  length
+                ora  length+1
+                beq  _zero
+                ldy  length
+                ldx  #$ff
+_modified       stx  $ffff      ; modified
+                lda  _modified+1
+                clc
+                adc  #8
+                sta  _modified+1
+                bcc  +
+                inc  _modified+2
++               dey
+                bne  _modified
+_zero           ldx  P8ZP_SCRATCH_REG
+
+                ldy  separate_pixels
+                beq  _zero2
+                lda  _modified+1
+                sta  P8ZP_SCRATCH_W1
+                lda  _modified+2
+                sta  P8ZP_SCRATCH_W1+1
+                lda  _filled_right,y
+                ldy  #0
+                ora  (P8ZP_SCRATCH_W1),y
+                sta  (P8ZP_SCRATCH_W1),y
+                jmp  _zero2
+_filled_right   .byte  0, %10000000, %11000000, %11100000, %11110000, %11111000, %11111100, %11111110
+_zero2
+            }}
         }
     }
 
@@ -289,9 +358,9 @@ _y_lookup_hi    .byte  >_plot_y_values
 
     asmsub get_y_lookup(ubyte y @Y) -> uword @AY {
         %asm {{
-            lda  _y_lookup_lo,y
+            lda  internal_plot._y_lookup_lo,y
             pha
-            lda  _y_lookup_hi,y
+            lda  internal_plot._y_lookup_hi,y
             tay
             pla
             rts

compiler/res/prog8lib/cx16/gfx2.p8

@@ -315,7 +315,6 @@ _done
     sub line(uword @zp x1, uword @zp y1, uword @zp x2, uword @zp y2, ubyte color) {
         ; Bresenham algorithm.
         ; This code special-cases various quadrant loops to allow simple ++ and -- operations.
-        ; TODO rewrite this in optimized assembly
         if y1>y2 {
             ; make sure dy is always positive to have only 4 instead of 8 special cases
             swap(x1, x2)
@@ -335,6 +334,7 @@ _done
             return
         }
 
+        ; TODO rewrite the rest in optimized assembly
         word @zp d = 0
         ubyte positive_ix = true
         if dx < 0 {

docs/source/libraries.rst

@@ -76,9 +76,8 @@ graphics
 Monochrome bitmap graphics routines, fixed 320*200 resolution:
 
 - clearing the screen
-- drawing lines
-- drawing circles and discs (filled circles)
-- plotting individual pixels
+- drawing individual pixels
+- drawing lines, rectangles, filled rectangles, circles, discs
 
 This library is available both on the C64 and the Cx16.
 It uses the ROM based graphics routines on the latter, and it is a very small library because of that.

docs/source/todo.rst

@@ -2,7 +2,6 @@
 TODO
 ====
 
-- implement gfx2's rect, fillrect, horizontal_line and vertical_line in graphics modules as well. (and optimize bresenham line to use vert/horiz line if possible)
 - detect variables that are written but never read - mark those as unused too and remove them, such as uword unused = memory("unused222", 20) - also remove the memory slab allocation
 - hoist all variable declarations up to the subroutine scope *before* even the constant folding takes place (to avoid undefined symbol errors when referring to a variable from another nested scope in the subroutine)
 - make it possible to use cpu opcodes such as 'nop' as variable names by prefixing all asm vars with something such as '_'