0006340: Discourage output color depending on input alpha due to gl_dst_alpha - The Dark Mod Bugtracker

ID	Project	Category	View Status	Date Submitted	Last Update

0006340	The Dark Mod	Graphics	public	14.11.2023 19:50	10.12.2023 11:25

Reporter	stgatilov	Assigned To	stgatilov
Priority	normal	Severity	minor	Reproducibility	sometimes
Status	resolved	Resolution	fixed
Product Version	TDM 2.11
Target Version	TDM 2.12	Fixed in Version	TDM 2.12

Summary	0006340: Discourage output color depending on input alpha due to gl_dst_alpha
Description	After some chatting with artists/mappers, it seems that they don't understand what gl_dst_alpha does and what perils it brings. The current framebuffer has alpha channel, which is filled with undefined garbage at any moment. This garbage is often just 1.0, but sometimes it can drop below that, or highly above that. If color output after rendering material depends on alpha before rendering it, then visual look of the material depends on previously rendered (independent) objects in undefined way. This should never happen. The only proper usage of gl_dst_alpha is when you certainly generate alpha channel in some prior stage of the same material. This usage is even described in iddevnet (section "Shaders in Materials" in https://iddevnet.dhewm3.org/doom3/materials.html). Most likely we should produce a warning if such a material is used.
Tags	No tags attached.

stgatilov 14.11.2023 20:09 administrator ~0016177	Implemented in svn rev 10506. Here is the list of materials generating the warning in load_all/materials.map: WARNING:material 'textures/darkmod/metal/flat/tiling_1d/gen_smooth_gold01' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/metal/flat/tiling_1d/gen_smooth_gold01_ns' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/metal/flat/tiling_1d/gen_smooth_silver01' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern01_centerrose_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern01_centersun_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern01_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern02_checker_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern02_crosshair_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern02_rings_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern02_star02_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/stone/flat/smooth/marble_pattern02_star_polished' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/window/ornate/stainglass_saint_01' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/window/ornate/stainglass_saint_02' output color depends on input alpha (0006340) WARNING:material 'textures/darkmod/window/ornate/stainglass_saint_03' output color depends on input alpha (0006340) WARNING:material 'textures/water_source/water_fake_reflect' output color depends on input alpha (0006340) WARNING:material 'textures/water_source/water_fake_reflect_02' output color depends on input alpha (0006340)

stgatilov 18.11.2023 10:34 administrator ~0016180 Last edited: 18.11.2023 10:39	Fixed the warnings in svn rev 16846 and rev 16487. Note that stainglass_saint_0x materials look differently, because env-mapped stage now has 2x less effect. Previously it had dst_alpha = 2 which caused the effect to have double magnitude. Unfortunately, there is no mapper-controlled multiplier on bumpmapped and envmapped material stage. One can in principle copy/paste the stage 2 times to replicate the old effect, but I decided to NOT do it yet.

Date Modified	Username	Field	Change
14.11.2023 19:50	stgatilov	New Issue
14.11.2023 19:50	stgatilov	Status	new => assigned
14.11.2023 19:50	stgatilov	Assigned To	=> stgatilov
14.11.2023 20:09	stgatilov	Note Added: 0016177
18.11.2023 10:34	stgatilov	Note Added: 0016180
18.11.2023 10:34	stgatilov	Status	assigned => resolved
18.11.2023 10:34	stgatilov	Resolution	open => fixed
18.11.2023 10:34	stgatilov	Fixed in Version	=> TDM 2.12
18.11.2023 10:39	stgatilov	Note Edited: 0016180
10.12.2023 11:25	stgatilov	Relationship added	related to 0006354