Page 5 of 6
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 10:27 am
by dpJudas
There are mainly two advantages to premultiplied alpha. The first is the saved multiplication (probably not measurable on GPU nowadays, maybe a little bit in software). The second is that texture filtering works more correctly if it is premultiplied. When the alpha isn't premultiplied the color of a transparent pixel bleeds into the result when doing a linear sampling.
As example, lets say we have a red opaque and a blue transparent pixel next to each other: rgba(1,0,0,1) and rgba(0,0,1,0). With linear sampling halfway through (50% of each) we get:
Code: Select all
sampled.r = p0.r * 0.5 + p1.r * 0.5 = 0.5
sampled.g = p0.g * 0.5 + p1.g * 0.5 = 0
sampled.b = p0.b * 0.5 + p1.b * 0.5 = 0.5
sampled.a = p0.a * 0.5 + p1.a * 0.5 = 0.5
If the colors are premultiplied, the textures will contain rgba(1,0,0,0) and rgba(0,0,0,0). That will give this sampling:
Code: Select all
sampled.r = p0.r * 0.5 + p1.r * 0.5 = 0.5
sampled.g = p0.g * 0.5 + p1.g * 0.5 = 0
sampled.b = p0.b * 0.5 + p1.b * 0.5 = 0
sampled.a = p0.a * 0.5 + p1.a * 0.5 = 0.5
Which results in a clean blend to transparent without any artifacts. That is the main reason that premultiplied alpha is so widespread rather than speed.
Btw. I wasn't aware that zdoom sometimes discarded the alpha channel. Under what conditions does this happen - always with one sided walls? Maybe I just haven't seen a map yet where there was transparent pixels in such a one-sided wall. You're right that in such a situation premultiplied alpha wouldn't work.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 10:54 am
by Graf Zahl
Any texture being put on a one-sided wall, on the upper or lower part of a two-sided wall or a non-3D-floor flat will always be drawn without alpha blending. Even fully transparent parts will be rendered black.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 10:56 am
by Graf Zahl
dpJudas wrote:
As example, lets say we have a red opaque and a blue transparent pixel next to each other: rgba(1,0,0,1) and rgba(0,0,1,0). With linear sampling halfway through (50% of each) we get:
Code: Select all
sampled.r = p0.r * 0.5 + p1.r * 0.5 = 0.5
sampled.g = p0.g * 0.5 + p1.g * 0.5 = 0
sampled.b = p0.b * 0.5 + p1.b * 0.5 = 0.5
sampled.a = p0.a * 0.5 + p1.a * 0.5 = 0.5
If the colors are premultiplied, the textures will contain rgba(1,0,0,0) and rgba(0,0,0,0). That will give this sampling:
Code: Select all
sampled.r = p0.r * 0.5 + p1.r * 0.5 = 0.5
sampled.g = p0.g * 0.5 + p1.g * 0.5 = 0
sampled.b = p0.b * 0.5 + p1.b * 0.5 = 0
sampled.a = p0.a * 0.5 + p1.a * 0.5 = 0.5
Which results in a clean blend to transparent without any artifacts. That is the main reason that premultiplied alpha is so widespread rather than speed.
There's still artifacts, but less severe. In GZDoom I added a simple filter to fully get rid of them and give all fully transparent edge pixels the color of one of their neighboring pixels.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 11:14 am
by dpJudas
Okay since it sounds zdoom relies on this quite a bit I'll have to change the code to not use premultiplied alpha. I don't think it will affect the performance much. I just generally use premultiplied alpha unless there's good reasons not to. In this case there seems to be.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 11:19 am
by Graf Zahl
Maybe it makes sense to use
bool FTexture::SmoothEdges(unsigned char * buffer,int w, int h)
from GZDoom here, if you are doing some filtering, to reduce the artifacts.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 3:36 pm
by dpJudas
Good idea. I do have a linear filter mode that can be toggled on where it would be useful.
Re: Truecolor software rendering
Posted: Sun Aug 07, 2016 11:42 pm
by cortlong50
have you ever felt dumb as shit reading something that went way over your head and so you just kinda exit the forum and hope nobody notices?
thats my cue.
Re: Truecolor software rendering
Posted: Mon Aug 08, 2016 5:15 am
by Edward-san
I got some time to try the truecolor branch again, but I got this asan error whenever I opened doom2 map01:
Code: Select all
==27141==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7f8ed74dd2b0 at pc 0x000000f164e7 bp 0x7ffe61b43b70 sp 0x7ffe61b43b60
READ of size 4 at 0x7f8ed74dd2b0 thread T0
#0 0xf164e6 in FTexture::GenerateBgraMipmaps()::Color4f::operator+(Color4f const&) const (/home/edward-san/zdoom/branch/truecolor/debug/gcc/zdoom+0xf164e6)
#1 0xf17ab8 in FTexture::GenerateBgraMipmaps() /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:486
#2 0xf161ce in FTexture::GenerateBgraFromBitmap(FBitmap const&) /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:376
#3 0xf15363 in FTexture::GetPixelsBgra() /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:205
#4 0x690391 in WallscanSampler::WallscanSampler(int, float, double, int, FTexture*, unsigned char const* (*)(FTexture*, int)) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1162
#5 0x693530 in wallscan_any(int, int, short*, short*, float*, int*, double, unsigned char const* (*)(FTexture*, int), void (*)(int, unsigned int (*&)(), void (*&)())) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1427
#6 0x694792 in wallscan(int, int, short*, short*, float*, int*, double, unsigned char const* (*)(FTexture*, int)) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1528
#7 0x695630 in call_wallscan /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1626
#8 0x6979f8 in R_RenderSegLoop() /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1871
#9 0x69f142 in R_StoreWallRange(int, int) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:2580
#10 0x5c92e1 in R_ClipWallSegment(int, int, bool) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:180
#11 0x5ccbb6 in R_AddLine(seg_t*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:769
#12 0x5d307c in R_Subsector(subsector_t*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1356
#13 0x5d33bc in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1396
#14 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#15 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#16 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#17 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#18 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#19 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#20 0x674590 in R_RenderActorView(AActor*, bool) /home/edward-san/zdoom/branch/truecolor/src/r_main.cpp:900
#21 0x5c487c in FSoftwareRenderer::RenderView(player_t*) /home/edward-san/zdoom/branch/truecolor/src/r_swrenderer.cpp:174
#22 0x8dab32 in D_Display() /home/edward-san/zdoom/branch/truecolor/src/d_main.cpp:770
#23 0x8dcadb in D_DoomLoop() /home/edward-san/zdoom/branch/truecolor/src/d_main.cpp:1013
#24 0x8e3c91 in D_DoomMain() /home/edward-san/zdoom/branch/truecolor/src/d_main.cpp:2642
#25 0x5b8ecd in main /home/edward-san/zdoom/branch/truecolor/src/posix/sdl/i_main.cpp:317
#26 0x7f8ef3ae882f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
#27 0x5aa0e8 in _start (/home/edward-san/zdoom/branch/truecolor/debug/gcc/zdoom+0x5aa0e8)
0x7f8ed74dd2b0 is located 0 bytes to the right of 174768-byte region [0x7f8ed74b2800,0x7f8ed74dd2b0)
allocated by thread T0 here:
#0 0x7f8ef6e04532 in operator new(unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x99532)
#1 0xf1bb72 in allocate /usr/include/c++/5/ext/new_allocator.h:104
#2 0xf1ba96 in allocate /usr/include/c++/5/bits/alloc_traits.h:491
#3 0xf1b9ef in _M_allocate /usr/include/c++/5/bits/stl_vector.h:170
#4 0xf1b878 in _M_create_storage /usr/include/c++/5/bits/stl_vector.h:185
#5 0xf1b612 in _Vector_base /usr/include/c++/5/bits/stl_vector.h:136
#6 0xf1b453 in vector /usr/include/c++/5/bits/stl_vector.h:278
#7 0xf16d8b in FTexture::GenerateBgraMipmaps() /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:419
#8 0xf161ce in FTexture::GenerateBgraFromBitmap(FBitmap const&) /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:376
#9 0xf15363 in FTexture::GetPixelsBgra() /home/edward-san/zdoom/branch/truecolor/src/textures/texture.cpp:205
#10 0x690391 in WallscanSampler::WallscanSampler(int, float, double, int, FTexture*, unsigned char const* (*)(FTexture*, int)) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1162
#11 0x693530 in wallscan_any(int, int, short*, short*, float*, int*, double, unsigned char const* (*)(FTexture*, int), void (*)(int, unsigned int (*&)(), void (*&)())) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1427
#12 0x694792 in wallscan(int, int, short*, short*, float*, int*, double, unsigned char const* (*)(FTexture*, int)) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1528
#13 0x695630 in call_wallscan /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1626
#14 0x6979f8 in R_RenderSegLoop() /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:1871
#15 0x69f142 in R_StoreWallRange(int, int) /home/edward-san/zdoom/branch/truecolor/src/r_segs.cpp:2580
#16 0x5c92e1 in R_ClipWallSegment(int, int, bool) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:180
#17 0x5ccbb6 in R_AddLine(seg_t*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:769
#18 0x5d307c in R_Subsector(subsector_t*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1356
#19 0x5d33bc in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1396
#20 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#21 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#22 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#23 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#24 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#25 0x5d332d in R_RenderBSPNode(void*) /home/edward-san/zdoom/branch/truecolor/src/r_bsp.cpp:1387
#26 0x674590 in R_RenderActorView(AActor*, bool) /home/edward-san/zdoom/branch/truecolor/src/r_main.cpp:900
#27 0x5c487c in FSoftwareRenderer::RenderView(player_t*) /home/edward-san/zdoom/branch/truecolor/src/r_swrenderer.cpp:174
#28 0x8dab32 in D_Display() /home/edward-san/zdoom/branch/truecolor/src/d_main.cpp:770
#29 0x8dcadb in D_DoomLoop() /home/edward-san/zdoom/branch/truecolor/src/d_main.cpp:1013
SUMMARY: AddressSanitizer: heap-buffer-overflow ??:0 FTexture::GenerateBgraMipmaps()::Color4f::operator+(Color4f const&) const
Shadow bytes around the buggy address:
0x0ff25ae93a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0ff25ae93a10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0ff25ae93a20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0ff25ae93a30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0ff25ae93a40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0ff25ae93a50: 00 00 00 00 00 00[fa]fa fa fa fa fa fa fa fa fa
0x0ff25ae93a60: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0ff25ae93a70: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0ff25ae93a80: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0ff25ae93a90: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0ff25ae93aa0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Heap right redzone: fb
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack partial redzone: f4
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
==27141==ABORTING
Terminated sig=0x0d
Re: Truecolor software rendering
Posted: Mon Aug 08, 2016 8:07 am
by dpJudas
cortlong50 wrote:have you ever felt dumb as shit reading something that went way over your head and so you just kinda exit the forum and hope nobody notices?
thats my cue.
I wouldn't feel bad it. There are other threads where I barely know what they are talking about either.
Re: Truecolor software rendering
Posted: Mon Aug 08, 2016 8:12 am
by dpJudas
Edward-san wrote:I got some time to try the truecolor branch again, but I got this asan error whenever I opened doom2 map01:
Buffer overflow in the mipmap generator code? Time for me to add some asserts! Thanks for making me aware of it.
Re: Truecolor software rendering
Posted: Sun Aug 21, 2016 10:53 pm
by enderkevin13
This sounds like it could be a great idea!
Re: Truecolor software rendering
Posted: Sun Aug 21, 2016 11:59 pm
by dpJudas
A quick update on this PR: I've completed the changes requested by Graf and fixed the buffer overrun identified by Edward-san.
Re: Truecolor software rendering
Posted: Thu Sep 22, 2016 8:53 am
by Major Cooke
I gave this a try out and damn... This is actually pretty awesome how it turned out. This surely is one way of bridging the gap a little closer to GZDoom (even though it's still quite far off).
Re: Truecolor software rendering
Posted: Tue Sep 27, 2016 8:11 am
by Gamer With Dignity
Can I expect this to be patched into a zdoom update in the near future?
Re: Truecolor software rendering
Posted: Tue Sep 27, 2016 10:29 am
by Rachael
You ... really want to "expect" that?