Normal Map Technical Details - Revision history

EricChadwick: /* Object-space normal map */

2023-12-04T12:22:22Z

‎Object-space normal map

EricChadwick: /* Tangent-Space vs. Object-Space */

2023-12-04T12:19:58Z

‎Tangent-Space vs. Object-Space

EricChadwick: /* Object-space normal map */ Mirroring link

2020-06-25T17:08:01Z

‎Object-space normal map: Mirroring link

EricChadwick: /* Tangent Basis */ MikkTspace, alphabetized methods

2019-04-27T16:38:03Z

‎Tangent Basis: MikkTspace, alphabetized methods

EricChadwick: /* Tangent Basis */

2018-04-17T17:31:02Z

‎Tangent Basis

EricChadwick: /* Tangent Basis */ rearranged for clarity

2018-04-17T17:29:49Z

‎Tangent Basis: rearranged for clarity

Dustinbrown at 22:54, 8 February 2017

2017-02-08T22:54:28Z

EricChadwick: Is my tangent basis un-synced?

2016-09-03T14:08:19Z

Is my tangent basis un-synced?

EricChadwick: /* RGB Channels */ compression format link fix, Swizzling.

2016-08-05T00:26:06Z

‎RGB Channels: compression format link fix, Swizzling.

EricChadwick: Synced tangent basis workflow from 3ds Max to Unity 5?

2016-08-04T17:34:31Z

Synced tangent basis workflow from 3ds Max to Unity 5?

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 Another way to explain these two types is to show how the spaces are oriented:
-[[image:normalmap_orientations.jpg|frame|none|Axis orientations for the two types of normal maps. <br>Image by [http://gerbenpasjes.com Gerben Pasjes].]]
+[[image:normalmap_orientations.png|frame|none|Axis orientations for the two types of normal maps. <br>Image by [http://gerbenpasjes.com Gerben Pasjes].]]
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 * Harder to overlay painted details because the base colors vary across the surface of the mesh. Painted details must be converted into Object Space to be combined properly with the OS map.
 * They don't compress very well, since the blue channel can't be recreated in the shader like with tangent-space maps. Also the three color channels contain very different data which doesn't compress well, creating many artifacts. Using a half-resolution object-space map is one option.
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@@ Line 75: / Line 75: @@
 Cons:
 * Can't easily reuse maps, different mesh shapes require unique maps.
-* Difficult to tile properly, and mirroring requires specific shader support.
+* Difficult to tile properly, and [http://polycount.com/discussion/53986 mirroring requires specific shader support].
 * Harder to overlay painted details because the base colors vary across the surface of the mesh. Painted details must be converted into Object Space to be combined properly with the OS map.
 * They don't compress very well, since the blue channel can't be recreated in the shader like with tangent-space maps. Also the three color channels contain very different data which doesn't compress well, creating many artifacts. Using a half-resolution object-space map is one option.

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 Each vertex in the tangent basis is a combination of three things: the mesh vertex's normal (influenced by smoothing), the vertex's tangent (usually derived from the V texture coordinate), and the vertex's bitangent (derived in code, also called the binormal). These three vectors create an axis for each vertex, giving it a specific orientation in the tangent space. These axes are used to properly transform the incoming lighting from world space into tangent space, so your normal-mapped model will be lit correctly.
-Unfortunately for artists, there are many different ways to calculate the tangent basis: [http://area.autodesk.com/blogs/chris/how_the_3ds_max_scanline_renderer_computes_tangent_and_binormal_vectors_for_normal_mapping 3ds Max], [http://download.autodesk.com/us/maya/2011help/index.html?url=./files/Appendix_A_Tangent_and_binormal_vectors.htm,topicNumber=d0e227193 Maya], [http://www.codesampler.com/dx9src/dx9src_4.htm#dx9_dot3_bump_mapping DirectX 9], [http://www.nvidia.com/object/NVMeshMender.html NVMeshMender], [http://www.terathon.com/code/tangent.html Eric Lengyel], a custom solution, etc. This means a normal map baked in one application probably won't shade correctly in another. Artists must do some testing with different [[Texture Baking|baking tools]] to find which works best with their output. When the renderer (or game engine) renders your game model, [[Shaders|the shader]] must use the same tangent basis as the normal map baker, otherwise you'll get incorrect lighting, especially across the seams between UV shells.
+Unfortunately for artists, there are many different ways to calculate the tangent basis: [https://github.com/dfelinto/blender/blob/master/intern/mikktspace/mikktspace.h MikkTspace] is the most common, but many others exist: [http://area.autodesk.com/blogs/chris/how_the_3ds_max_scanline_renderer_computes_tangent_and_binormal_vectors_for_normal_mapping 3ds Max], [http://www.codesampler.com/dx9src/dx9src_4.htm#dx9_dot3_bump_mapping DirectX 9], [http://www.terathon.com/code/tangent.html Eric Lengyel], [http://download.autodesk.com/us/maya/2011help/index.html?url=./files/Appendix_A_Tangent_and_binormal_vectors.htm,topicNumber=d0e227193 Maya], [http://www.nvidia.com/object/NVMeshMender.html NVMeshMender], etc. This means a normal map baked in one application probably won't shade correctly in another. Artists must do some testing with different [[Texture Baking|baking tools]] to find which works best with their output. When the renderer (or game engine) renders your game model, [[Shaders|the shader]] must use the same tangent basis as the normal map baker, otherwise you'll get incorrect lighting, especially across the seams between UV shells.
 The [http://www.xnormal.net/ xNormal] SDK supports custom tangent basis methods. When a programmer uses it to implement their renderer's own tangent basis, artists can then use Xnormal to bake normal maps that will match their renderer perfectly.

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 == Tangent Basis ==
-[[Normal_Map_Technical_Details#Tangent-Space_vs._Object-Space|Tangent-space]] normal maps use a special kind of vertex data called the ''tangent basis''. This is similar to UV coordinates except it provides directionality across the surface. It forms a surface-relative coordinate system for the per-pixel normals stored in the normal map. To light a normal-mapped surface, a coordinate system like this is required.
+[[Normal_Map_Technical_Details#Tangent-Space_vs._Object-Space|Tangent-space]] normal maps use a special kind of vertex data called the ''tangent basis''. This is similar to UV coordinates except it provides directionality across the surface. It's a surface-relative coordinate system for the per-pixel normals stored in the normal map, so lighting can be applied to the normal-mapped surface.
 Light rays are in world space, but the normals stored in the normal map are in tangent space. When the model is being rendered, the light rays must be converted from world space into tangent space, using the tangent basis to get there. At that point the incoming light rays are compared against the directions of the normals in the normal map, and this determines how much each pixel is going to be lit. Alternatively, instead of converting the light rays some shaders will convert the normals in the normal map from tangent space into world space. Then those world-space normals are compared against the light rays, and the model is lit appropriately. The method depends on who wrote the shader, but the end result is the same. Both methods require a tangent basis to transform the lighting.

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 == Common Swizzle Coordinates ==
-D Software capable of displaying tangent space normal maps will have a native required direction, or "handedness" for the RGB channels in a normal map, sometimes referred to as "Swizzle Coordinates," though [[Shaders]] can often be written to override this native handedness. You may hear developers refer to "flipping the green channel" in order to get a normal map to display correctly, and this simply indicates that when the normal map was baked, it was authored with the incorrect handedness in the green channel. Left/Down handedness is indicated with a negative (-), and right/up handedness is demarcated with a (+) positive.
+D Software capable of displaying tangent space normal maps will have a native required direction, or "handedness" for the RGB channels in a normal map, sometimes referred to as "Swizzle Coordinates," though [[Shaders]] can often be written to override this native handedness. You may hear developers refer to "flipping the green channel" in order to get a normal map to display correctly, and this simply indicates that when the normal map was baked, it was authored with the incorrect handedness in the green channel. Right handedness, which coincides with OpenGL is indicated with a plus sign (ex. +Y), whereas Left handedness, which coincides with DirectX, is indicated with a negative sign (ex. -Y)
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 [http://www.handplane3d.com/ Handplane] is a free utility that converts an object-space normal map + model into different tangent spaces. This allows a synced workflow with various tools.
-[http://polycount.com/discussion/174385/synced-tangent-basis-workflow-from-3ds-max-to-unity-5 Synced tangent basis workflow from 3ds Max to Unity 5?] Polycount Forum thread.
+* [http://polycount.com/discussion/174385/synced-tangent-basis-workflow-from-3ds-max-to-unity-5 Synced tangent basis workflow from 3ds Max to Unity 5?] Polycount Forum thread.
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 If you see lighting coming from the wrong angle when you're looking at your normal-mapped model, and the model is using a tangent-space normal map, the normal map shader might be expecting the red or green channel (or both) to point in the opposite direction. To fix this either change the shader, or simply invert the appropriate color channels in an image editor, so that the black pixels become white and the white pixels become black.
-Some shaders expect the color channels to be swapped or re-arranged to work with a particular [[#NormalMapCompression|compression format]]. For example the DXT5_nm format usually expects the X axis to be in the alpha channel, the Y axis to be in the green channel, and the red and blue channels to be empty.
+Some shaders expect the color channels to be swapped or re-arranged to work with a particular [[Normal Map Compression|compression format]]. This re-arranging of the normal map axes is called [[ChannelPacking#Swizzle|swizzling]]. For example the DXT5_nm format usually expects the X axis to be in the alpha channel, the Y axis to be in the green channel, and the red and blue channels to be empty.
 == Tangent Basis ==

← Older revision		Revision as of 17:34, 4 August 2016
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	[http://www.handplane3d.com/ Handplane] is a free utility that converts an object-space normal map + model into different tangent spaces. This allows a synced workflow with various tools.		[http://www.handplane3d.com/ Handplane] is a free utility that converts an object-space normal map + model into different tangent spaces. This allows a synced workflow with various tools.

		+	[http://polycount.com/discussion/174385/synced-tangent-basis-workflow-from-3ds-max-to-unity-5 Synced tangent basis workflow from 3ds Max to Unity 5?] Polycount Forum thread.

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