gfx2 optimizations for vertical lines

compiler/res/prog8lib/cx16/gfx2.p8

@@ -212,15 +212,21 @@ _done
 
     sub vertical_line(uword x, uword y, uword height, ubyte color) {
         if active_mode==1 {
-            ; TODO for the 320x256 8bbp mode use vera auto increment
-            repeat lsb(height) {
-                plot(x, y, color)
-                y++
-            }
+            position(x,y)
+            ; set vera auto-increment to 320 pixel increment (=next line)
+            cx16.VERA_ADDR_H = (cx16.VERA_ADDR_H & %00000111) | (14<<4)
+            %asm {{
+                ldy  height
+                lda  color
+-               sta  cx16.VERA_DATA0
+                dey
+                bne  -
+            }}
             return
         }
 
         ; note for the 1 bpp modes we can't use vera's auto increment mode because we have to 'or' the pixel data in place.
+        ; TODO optimize by manually advancing the vera's data pointer (note stipple and black color!)
         repeat height {
             plot(x, y, color)
             y++

examples/cx16/testgfx2.p8

@@ -7,7 +7,7 @@
 main {
 
     sub start() {
-        gfx2.screen_mode(1)
+        gfx2.screen_mode(128)
 
         uword pixels = memory("pixels", 320)
         uword yy = 10
@@ -16,8 +16,8 @@ main {
         uword cnt
         pp=pixels
 
-        for xx in 10 to 300 {
-            gfx2.vertical_line(xx, 10, 220, 1)
+        for xx in 0 to 639 {
+            gfx2.vertical_line(xx, 0, 480, 1)
         }
         gfx2.screen_mode(255)
         txt.print("done!\n")