Straight view volume box fix

[AdamPlenty]

Fixes #5097
Fixes #5120

Tested at 320x200, 640x480, 1280x800, and 1920x1080 resolutions.

[cerwym]

Rather than accepting it, why did you choose 15 specifically, what you're doing there is changing the depth offset to stop occlusion in the bucket, honestly, I would prefer it if you made a reasonable review on what in the bucket occludes this.

Note : I've removed this entirely in the new renderer

[cerwym]

Need deets

[Copilot]

Pull request overview

This PR adjusts the straight/front view volume box rendering so the highlight/volume box outline appears consistent across resolutions, addressing the visual artifacts reported in #5097 and #5120.

Changes:

• Tweaks the Z-offset used when drawing both the normal and “fancy” frontview map volume boxes.
• Aligns the two frontview volume-box rendering paths to use the same updated offset.

Suppressed comments (1)

src/engine_render.c:8567

• The rounding adjustment in y_start/y_end and x_start/x_end uses ((a % b) >= b) which can never be true for non-negative values, so the ternary is dead code. This is misleading and makes it harder to reason about the pixel-to-slab mapping (especially when debugging resolution-specific artifacts).

    coord_z -= (15 * (long)stl_width) >> 2;
    for (int roomspace_y = 0; roomspace_y < room_slab_height; roomspace_y += 1)
    {
        int y_start = (box_height * roomspace_y       / room_slab_height) + ((((box_height * roomspace_y)       % room_slab_height) >= room_slab_height) ? 1 : 0);
        int y_end =   (box_height * (roomspace_y + 1) / room_slab_height) + ((((box_height * (roomspace_y + 1)) % room_slab_height) >= room_slab_height) ? 1 : 0);

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[AdamPlenty]

Rather than accepting it, why did you choose 15 specifically, what you're doing there is changing the depth offset to stop occlusion in the bucket, honestly, I would prefer it if you made a reasonable review on what in the bucket occludes this.

Note : I've removed this entirely in the new renderer

I've no idea; I just tried it arbitrarily and it seemed to work, so I went with it. My previous fix only fixed the top line.

[AdamPlenty]

Need deets

What do you mean?

[Loobinex]

Now you can see the box through walls:

[AdamPlenty]

Now you can see the box through walls:

I don't have this issue... ...with most walls.

[AdamPlenty]

Only seems to happen if there's a path visible on the other side.