Line code

[stan cartwright]

I looked up Bresenham's line algo and there'a a basic..just basic,not bbc basic or commodore basic but it converted easy to gcb. I did it because I had wanted to draw lines slowly ie a pixel every program loop.
It was for a game.
Anyway the code is simple and fast. I am amazed it worked and understand integer variables better.... the minus variables.
https://www.youtube.com/watch?v=r0qR1BwdXf0&feature=youtu.be

#chip mega328p,16
#option explicit
#include <glcd.h>
#include <uno_mega328p.h >

    #define GLCD_TYPE GLCD_TYPE_ILI9341

    'Pin mappings for SPI - this GLCD driver supports Hardware SPI and Software SPI
    #define GLCD_DC       DIGITAL_8         ' Data command line
    #define GLCD_CS       DIGITAL_10          ' Chip select line
    #define GLCD_RESET    DIGITAL_9         ' Reset line

    #define GLCD_DI       DIGITAL_12          ' Data in | MISO    - Not used therefore not really required
    #define GLCD_DO       DIGITAL_11          ' Data out | MOSI
    #define GLCD_SCK      DIGITAL_13          ' Clock Line
GLCDRotate ( Landscape_Rev )
GLCDCLS ILI9341_Black

 dim dx,dy,sx,sy,er,e2 as integer
 dim x2,x1,y1,y2 as word

 x1=random :y1=random:x2=random:y2=random

 ;this the draw line routine
draw:
 DX = ABS(X2 - X1):SX = -1:IF X1 < X2 THEN SX = 1
 DY = ABS(Y2 - Y1):SY = -1:IF Y1 < Y2 THEN SY = 1
 ER = -DY:IF DX > DY THEN ER = DX
 ER = ER / 2
 pixel:
 pset X1,Y1,ILI9341_WHITE
 IF X1 = X2 AND Y1 = Y2 THEN x1=x2:y1=y2:x2=random:y2=random:goto draw
 E2 = ER
 IF E2 > -DX THEN ER = ER - DY:X1 = X1 + SX
 IF E2 < DY THEN ER = ER + DX:Y1 = Y1 + SY
 GOTO pixel

slow cos of using random

[stan cartwright]

so short. got rid of x1=x2 and y1=y2 as it wasted a test every loop.
Getting rid of the goto ...I gave up.
This is pretty fast. how to time it draw 1000 lines and compare to glcd

sub draw (in x1,in y1,in x2,in y2,in colour)
 DX = ABS(X2 - X1):SX = -1:IF X1 < X2 THEN SX = 1
 DY = ABS(Y2 - Y1):SY = -1:IF Y1 < Y2 THEN SY = 1
 ER = -DY:IF DX > DY THEN ER = DX
 ER = ER / 2
pixel:
pset X1,Y1,colour
if x1=x2 then
  if y1=y2 then return
end if
 E2 = ER
 IF E2 > -DX THEN ER = ER - DY:X1 = X1 + SX
 IF E2 < DY THEN ER = ER + DX:Y1 = Y1 + SY
GOTO pixel

[stan cartwright]

the line draw in glcd.h is longer

Sub Line(In LineX1 as word, In LineY1 as word, In LineX2 as word, In LineY2 as word, Optional In LineColour as word = GLCDForeground)

      dim LineStepX as integer
      dim LineStepY as integer
      dim LineDiffX, LineDiffY as integer
      dim LineDiffX_x2, LineDiffY_x2 as integer
      dim LineErr as integer



      LineDiffX = 0
      LineDiffY = 0
      LineStepX = 0
      LineStepY = 0
      LineDiffX_x2 = 0
      LineDiffY_x2 = 0
      LineErr = 0


      LineDiffX =  LineX2 -   LineX1
      LineDiffY =  LineY2 -   LineY1

      if (LineDiffX > 0) then
              LineStepX = 1
      else
              LineStepX = -1
      end if

      if (LineDiffY > 0) then
          LineStepY = 1
       else
          LineStepY = -1
      end if

      LineDiffX = LineStepX * LineDiffX
      LineDiffY = LineStepY * LineDiffY

      LineDiffX_x2 = LineDiffX*2
      LineDiffY_x2 = LineDiffY*2

      if ( LineDiffX >= LineDiffY) then

          LineErr = LineDiffY_x2 - LineDiffX

          do while (   LineX1 <>  LineX2 )

              PSet (   LineX1,   LineY1, LineColour )
              LineX1 += LineStepX
              if ( LineErr < 0) then
                  LineErr += LineDiffY_x2
              else
                  LineErr += ( LineDiffY_x2 - LineDiffX_x2 )
                  LineY1 += LineStepY
              end if
          loop

          PSet (   LineX1,   LineY1, LineColour )
      else

          LineErr = LineDiffX_x2 - LineDiffY
          do while (   LineY1 <>  LineY2)
              PSet (   LineX1,   LineY1, LineColour )
              LineY1 += LineStepY
              if ( LineErr < 0) then
                  LineErr += LineDiffX_x2
               else
                  LineErr += ( LineDiffX_x2 - LineDiffY_x2 )
                  LineX1 += LineStepX
              end if
          loop
          PSet (   LineX1,   LineY1, LineColour )

      end if



end sub

[stan cartwright]

In my code there's er=er/2. would rotate er right simple be faster?
it's in the init not the main loop so only occurs once but if I draw lots of lines it might matter.
the init in the glcd line uses multiply a few times.

[stan cartwright]

seems gcb line drew a line 17.19 times a second
and mine 16.88 times a second.