Rendering artifacts at different viewport sizes

[zear]

Deathrace exhibits multiple issues related to rendering the 3d part of the screen in non-full resolution (i.e. manipulating the viewport size with -/+ keys):

1. Depth buffer

When the gRender_screen is scaled such that it doesn't match dimensions of gBack_screen, the depth buffer's position and size differs from the color buffer, causing visible artifacts on the screen:

2. Blending

The viewport height passed to the shader should be the one of the renderer, not the color buffer. Otherwise, geometry behind transparent materials is sampled at the wrong y offset:

3. Blending in map mode

When map mode is enabled, the scene is rendered thrice to a single frame. This breaks blending in GL renderer, which depends on a clear depth buffer. The result is fully opaque transparencies:

4. External sky

Depending on the screen size, something seems to obstruct different parts of the external sky:

https://user-images.githubusercontent.com/510643/213887149-ec42931d-8d5b-4891-949f-cbcfd60c602b.mp4

Currently, I can't tell whether this is geometry, or the sky bitmap not rendering properly.

[zear]

Parts 1-3 are now fixed in https://github.com/dethrace-labs/dethrace/pull/283.

[zear]

Regarding part 4, it is the chunk of ExternalSky code responsible for filling in the background with uniform color around the sky pixelmap that is at fault. After a change to draw in white, everything becomes clear:

https://user-images.githubusercontent.com/510643/213915480-20f67a8c-1386-46a6-871a-388aaaa9bbc6.mp4

Now, the reason this happens is because the below code doesn't take pRender_buffer->base_x/pRender_buffer->base_y into account while calculating DRPixelmapRectangleFill offsets:

https://github.com/dethrace-labs/dethrace/blob/83ba373426385882fdf098ce363bb0cf6ea2e71c/src/DETHRACE/common/depth.c#L498-L506

This can be easily fixed by respecting said offsets:

    /* Viewport offsets - added by Dethrace. */
    int off_x = 0;
    int off_y = 0;

(...)

#if defined(DETHRACE_FIX_BUGS)
    /* Take viewport offsets into account. */
    off_x = pRender_buffer->base_x;
    off_y = pRender_buffer->base_y;
#endif

    if (top_y > 0) { 
        top_col = ((tU8*)col_map->pixels)[0]; 
        DRPixelmapRectangleFill(pRender_buffer, off_x + -pRender_buffer->origin_x, off_y + -pRender_buffer->origin_y, pRender_buffer->width, top_y, top_col); 
    } 
    bot_height = pRender_buffer->height - pRender_buffer->origin_y - hori_y - col_map->height; 
    if (bot_height > 0) { 
        bot_col = ((tU8*)col_map->pixels)[col_map->row_bytes * (col_map->height - 1)]; 
        DRPixelmapRectangleFill(pRender_buffer, off_x + -pRender_buffer->origin_x, off_y + hori_y + col_map->height, pRender_buffer->width, bot_height, bot_col); 
    } 

However, the OG does not do that. I wonder why it works for them - they still keep track of base_x/base_y and update those fields in AdjustRenderScreenSize, so those values are most definitely not 0 at the time ExternalSky is called. And yet, the sky is rendered just fine.

@dethrace-labs @madebr Should we debug this deeper, or is the above solution satisfactory for now?

[dethrace-labs]

Fixed with software renderer