BGE Material - Alpha Blend: Add - not respecting object.color alfa value #28888

New Issue

Pavel Křupala · 2011-10-12T12:23:20+02:00

Pavel Křupala commented

2011-10-12 12:23:20 +02:00

Category: Rendering

%%%Using:
Blender 2.59.4 with Addons-Contrib, Multi-Branch Merge from GraphicAll.org
Built with MSVC 2008 Express and Scons:

GSOC Pepper Branch merged to trunk!
GSOC Particles-2010 Branch merged to trunk!
GSOC BGE:Recast & Detour-2010 Branch merged to trunk!
GSOC Radish Branch merged to trunk!
Texface and Material game engine patch now in trunk!

Material:
Shadeless
Game Settings: Backface - Off, Alpha Blend: Add, Face Orientation: Billboard
Options: Object Color: ON
Transparency: On, Z Transparency, Alpha 0.0
1 Texture:
PNG with alfa channel, UV mapping on Plane, Influence: Color 1.0, Alfa 1.0

every time in script you change color through python script in game engine like:
obj.color = [1.0, 1.0, 1.0, 0.5]
Alpha Blend mode ADD does NOT respect alpha value of given color.
Every other Alpha Blend option does respect the alpha and works fine.

see .blend file, just layer 2 and press P to see the difference between 2 modes of Alpha Blending

PC:
i7-2600K
8GB Kingston Ram
Windows 7
nVidia GTX 560%%%

**Category**: Rendering %%%Using: Blender 2.59.4 with Addons-Contrib, Multi-Branch Merge from GraphicAll.org Built with MSVC 2008 Express and Scons: GSOC Pepper Branch merged to trunk! GSOC Particles-2010 Branch merged to trunk! GSOC BGE:Recast & Detour-2010 Branch merged to trunk! GSOC Radish Branch merged to trunk! Texface and Material game engine patch now in trunk! -------------- Material: Shadeless Game Settings: Backface - Off, Alpha Blend: Add, Face Orientation: Billboard Options: Object Color: ON Transparency: On, Z Transparency, Alpha 0.0 1 Texture: PNG with alfa channel, UV mapping on Plane, Influence: Color 1.0, Alfa 1.0 every time in script you change color through python script in game engine like: obj.color = [1.0, 1.0, 1.0, 0.5] Alpha Blend mode ADD does NOT respect alpha value of given color. Every other Alpha Blend option does respect the alpha and works fine. see .blend file, just layer 2 and press P to see the difference between 2 modes of Alpha Blending ---------- PC: i7-2600K 8GB Kingston Ram Windows 7 nVidia GTX 560%%%

Pavel Křupala commented

2011-10-12 12:23:20 +02:00

Changed status to: 'Open'

Dalai Felinto commented

2011-10-12 19:07:49 +02:00

%%%Hi Pavel,
it's not clear to me whether this is a new bug, or a functionality that was always missing.

Can you provide a sample file in 2.59 (or even 249)?
Also you don't need to zip the files. Saving the file with "compressed" turned on should be enough.%%%

%%%Hi Pavel, it's not clear to me whether this is a new bug, or a functionality that was always missing. Can you provide a sample file in 2.59 (or even 249)? Also you don't need to zip the files. Saving the file with "compressed" turned on should be enough.%%%

Pavel Křupala commented

2011-10-13 11:05:35 +02:00

%%%Hi, i cant answer the question if its bug or missing functionality, but sample file is in attachment in previous post that was done with 2.59.4 with the bge material patch, because original 2.59 version doesn't have the patch included.
I belive that it is a bug because when I was programming pure OpenGL i used transparency too with glBlendFunc(GL_SRC_ALPHA,GL_ONE) and GL_RGBA, Even if I had to manualy sort the particles to display the farthest first (sort by depth), but remember setting alpha value for particles/planes/textures was working...

In the demo file the correct behavior can be seen on the left particles - they are going up and fading (because of setting alpha value)
right particle system is set with Alpha blend ADD mode and alpha is set too, but you can see that particles are not fading out%%%

%%%Hi, i cant answer the question if its bug or missing functionality, but sample file is in attachment in previous post that was done with 2.59.4 with the bge material patch, because original 2.59 version doesn't have the patch included. I belive that it is a bug because when I was programming pure OpenGL i used transparency too with glBlendFunc(GL_SRC_ALPHA,GL_ONE) and GL_RGBA, Even if I had to manualy sort the particles to display the farthest first (sort by depth), but remember setting alpha value for particles/planes/textures was working... In the demo file the correct behavior can be seen on the left particles - they are going up and fading (because of setting alpha value) right particle system is set with Alpha blend ADD mode and alpha is set too, but you can see that particles are not fading out%%%

Daniel Stokes commented

2013-09-04 23:56:45 +02:00

%%%I am not sure this is actually a bug. The way add alpha works is to use a blending function that adds the source and destination RGBA values together. The reason changing the source alpha value (the particle) doesn't do anything is because the destination alpha is always 1. After the values are added together, they get clamped into the 0 to 1 range. This means using add alpha, the resulting alpha value will always be 1 regardless of the source alpha.

One problem you are running into with the particle image is that the transparent areas are white. If they are black you actually get circles instead of squares. Not sure if that is a problem with Blender image loading or not. This is also something that affects the viewport, so I don't see that as a BGE bug.%%%

%%%I am not sure this is actually a bug. The way add alpha works is to use a blending function that adds the source and destination RGBA values together. The reason changing the source alpha value (the particle) doesn't do anything is because the destination alpha is always 1. After the values are added together, they get clamped into the 0 to 1 range. This means using add alpha, the resulting alpha value will always be 1 regardless of the source alpha. One problem you are running into with the particle image is that the transparent areas are white. If they are black you actually get circles instead of squares. Not sure if that is a problem with Blender image loading or not. This is also something that affects the viewport, so I don't see that as a BGE bug.%%%

Inês Almeida commented

2014-06-17 11:45:21 +02:00

Changed status from 'Open' to: 'Archived'

Inês Almeida closed this issue

2014-06-17 11:45:21 +02:00

Inês Almeida commented

2014-06-17 11:45:21 +02:00

Added subscriber: @brita