Alpha blending - Revision history

Windwalkr at 10:16, 24 October 2017

2017-10-24T10:16:46Z

← Older revision		Revision as of 10:16, 24 October 2017
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	[[Alpha blending]] is a technique where a model is rendered as partially transparent. Without [[alpha blending]], each screen ~~pixel~~ affected by a given model is simply overwritten by the model's color at that location. With [[alpha blending]], a blend occurs between the ~~pixel~~'s original coloration and the model's color at that location. This blend is controlled by an opacity strength value, known as "alpha".		[[Alpha blending]] is a technique where a model is rendered as partially transparent. Without [[alpha blending]], each screen [[fragment]] affected by a given model is simply overwritten by the model's color at that location. With [[alpha blending]], a blend occurs between the fragment's original coloration and the model's color at that location. This blend is controlled by an opacity strength value, known as "alpha".

	There are two typical sources used to determine alpha while rendering; the first is a per-object alpha value set at runtime. The second is a per-texel value set in the [[~~diffuse~~ map]]. Each value ranges from 0.0 (fully transparent) to 1.0 (fully opaque.) These are multiplied together to give a per-~~pixel~~ alpha value used for blending.		There are two typical sources used to determine alpha while rendering; the first is a per-object alpha value set at runtime. The second is a per-texel value set in the [[albedo map]]. Each value ranges from 0.0 (fully transparent) to 1.0 (fully opaque.) These are multiplied together to give a per-fragment alpha value used for blending.

	[[Alpha blending]] is order dependent. If two objects using 50% alpha are rendered over the same ~~screen pixels~~, the result will include 25% of the original pixel color, 25% of the first object's color, and 50% of the second object's color. For this reason:		[[Alpha blending]] is order dependent. If two objects using 50% alpha are rendered over the same fragments, the result will include 25% of the original pixel color, 25% of the first object's color, and 50% of the second object's color. For this reason:

	* Alpha-blended objects are typically rendered last, after all opaque or alpha-masked objects have been rendered.		* Alpha-blended objects are typically rendered last, after all opaque or alpha-masked objects have been rendered.

Retro00064: Added Category:Texture mapping.

2011-09-05T02:03:35Z

Added Category:Texture mapping.

← Older revision		Revision as of 02:03, 5 September 2011
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	* Alpha-blended polygons which intersect other alpha-blended polygons will always be rendered incorrectly as Trainz does not split polygons.		* Alpha-blended polygons which intersect other alpha-blended polygons will always be rendered incorrectly as Trainz does not split polygons.
	* Alpha-blended objects are typically rendered without modifying the z-buffer. They still honor the z-buffer values written by opaque or alpha-masked objects.		* Alpha-blended objects are typically rendered without modifying the z-buffer. They still honor the z-buffer values written by opaque or alpha-masked objects.

			[[Category:Texture mapping]]

Windwalkr: 1 revision

2010-02-03T13:58:20Z

1 revision

← Older revision	Revision as of 13:58, 3 February 2010
(No difference)

Windwalkr at 23:57, 16 September 2008

2008-09-16T23:57:03Z

New page

[[Alpha blending]] is a technique where a model is rendered as partially transparent. Without [[alpha blending]], each screen pixel affected by a given model is simply overwritten by the model's color at that location. With [[alpha blending]], a blend occurs between the pixel's original coloration and the model's color at that location. This blend is controlled by an opacity strength value, known as "alpha".

There are two typical sources used to determine alpha while rendering; the first is a per-object alpha value set at runtime. The second is a per-texel value set in the [[diffuse map]]. Each value ranges from 0.0 (fully transparent) to 1.0 (fully opaque.) These are multiplied together to give a per-pixel alpha value used for blending.

[[Alpha blending]] is order dependent. If two objects using 50% alpha are rendered over the same screen pixels, the result will include 25% of the original pixel color, 25% of the first object's color, and 50% of the second object's color. For this reason:

* Alpha-blended objects are typically rendered last, after all opaque or alpha-masked objects have been rendered.
* Alpha-blended objects which can be seen through other alpha-blended objects need to be [[alpha sorting|alpha sorted]] in order of distance-from-observer to maintain correct visuals. (See. [http://en.wikipedia.org/wiki/Painter's_algorithm Painter's algorithm])
* Alpha-blended polygons which intersect other alpha-blended polygons will always be rendered incorrectly as Trainz does not split polygons.
* Alpha-blended objects are typically rendered without modifying the z-buffer. They still honor the z-buffer values written by opaque or alpha-masked objects.