A new sky

Example 1 - a simple sky image replacement

To render the image of a sky in DOOM/2/U, idSoftware used a system where the flat F_SKY1 is a placeholder

F_SKY1 (45K)

for the actual texture of the sky.

So, let's see what the simplest method is of replacing the sky image for a map in DOOM format.

Construct a simple map with a map editor of your choice

pic00 (77K)

and save it.

pic01 (61K) For the new sky I downloaded a picture from the internet and reworked it to a size of 256x128 pixels.

Then open your newly constructed map in Slade3 and drag/drop the new sky image in between P_START and P_END markers.

pic02 (127K)

rename the sky image to RSKY1, the same name as in DOOM2.WAD.

pic03 (127K)

Now, let's have a look what the sky looks like in-game.

To loop the video rightclick and select Loop

Uh, Oh, that does not look right. The sky is terribly segmented and repeats. Why is that happening?

The answers is simple enough, the image repeats because the DOOM engine draws the sky 4 times, once for each cardinal direction. And also the image itself must be tiled properly, so that the edges flow into each other without a noticable break.

To fix the tiling issue I loaded the image into Paint Shop Pro 7.04 by Jasc

pic04 (102K)

pic05 (59K)
tiling settings

pic06 (59K)
the resulting image

That done, let's redo the map and use the tiled sky image:

To loop the video rightclick and select Loop

While the tiling issue is resolved it is still noticable that the image repeats 4 times by looking at the star cloud. But, yes, that looks much better.

To recap
If you name the sky image RSKY1, RSKY2 or RSKY3 (for DOOM2) or SKY1, SKY2 or SKY3 (for DOOM), or SKY4 (for Ultimate DOOM) and keep the same size (256x128) as the original sky image, then there is no need to edit TEXTURE1 or PNAMES.

However, if the sky image is a different size, then TEXTURE1 and PNAMES have to be updated with the new patch. That is covered in another tutorial.

Happy fragging.
Kappes Buur, Jan 18, 2019