Applesoft BASIC Double Low Resolution Graphics

In the normal Lo-Res graphics mode, the screen resolution is 40x40 pixels.
The Double Lo-Res graphics mode is so named because the pixels along the X-axis are doubled to create a 80x40 pixel screen.

Lo-Res Colors (0 - 15)

0 black
1 red
2 Dark Blue
3 purple
4 Dark Green
5 Gray
6 medium blue
7 light blue
8 Brown
9 orange
10 gray
11 Pink
12 light green
13 Yellow
14 Aqua
15 white

On the IIc and IIgs, double lo-res can be accessed from Applesoft:

10 D$=CHR$(4)
20 PRINT D$;"PR#3" : REM 80-column mode
30 POKE 49246,0    : REM $C05E - enable double resolution graphics
40 GR              : REM Turn on double lo-res mode

Use the standard lo-res commands to draw.
The available drawing area is 80 columns and 40 or 48 rows.
The colours are identical to standard lo-res.
The SCRN function, which reads the color of a pixel at an X,Y coordinate, does not work properly in double lo-res.

Normal Lo-Res has a resolution of 40x40.

     ______________________________
    |(0,0)                   (39,0)|
    |                              |
    |                              | GRAPHICS
    |                              |
    |(0,39)                 (39,39)|
    |------------------------------|
    |HTAB  1                       | TEXT
    |VTAB 21                       | 4 rows
    |______________________________|

Double Lo-Res has a resolution of 80x40.

     ______________________________
    |(0,0)                   (79,0)|
    |                              |
    |                              | GRAPHICS
    |                              |
    |(0,39)                 (79,39)|
    |------------------------------|
    |HTAB  1                       | TEXT
    |VTAB 21                       | 4 rows
    |______________________________|

10 D$=CHR$(4)
20 PRINT D$;"PR#3" : REM 80-column mode
30 POKE 49246,0    : REM $C05E - enable double resolution graphics
40 GR : HOME       : GRaphics Mode

120 COLOR=1
130 HLIN 0,79 AT 0
135 COLOR=13
140 HLIN 0,79 AT 39
145 COLOR=12
150 VLIN 0,39 AT 0
155 COLOR=7
160 VLIN 0,39 AT 79

200 FOR X=1 TO 79 STEP 2
220 COLOR=14
230 Y=X/2
235 X1=X-1
236 PRINT X;" ";X1;" ";Y
240 PLOT X1,Y
245 PLOT X,Y
260 NEXT X

300 FOR X=1 TO 79 STEP 2
320 COLOR=15
330 Y=X/2
333 Y=39-INT(Y)
335 X1=X-1
336 PRINT X;" ";X1;" ";Y
340 PLOT X1,Y
345 PLOT X,Y
360 NEXT X