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Postlight

15 February 2007 87,605 views 3 Comments

FAQ

There follows a list of frequently asked questions about Post Light. Most of the answers can be found within this documentation, but are also presented here for conciseness. If you have any other questions, please don’t hesitate to get in touch so that I can add your question to this list.

Installation

  • Why can’t I find the Post Light plug-ins in the FXTree? View >

Scene Preparation

  • Will Post Light work with any render tree that I use for my object materials? View >
  • Will Post Light work with hair and particles? View >
  • Will Post Light work with transparency and refractions? View >
  • Will Post Light work with reflections? View >

Passes

  • What passes do I need? View >
  • Is there an easy way to make the passes? View >
  • Can I just use XSI’s standard (diffuse / specular / normal / etc.) pass? View >
  • Why don’t my bumps show up in the normal pass when I use the PostLightPhong Shader? View >

Usage

  • Why do I need the Post Light Monitor? View >
  • Why do I need the Post Light Encode tool? View >
  • What’s the difference between the two inputs on the Post Light Encode tool? View >
  • I’m getting annoyed. Everytime I change a setting I have to wait for Post Light to re-render.View >

Rendering

  • Why has Post Light rendered a black image? View >
  • Why doesn’t Post Light react to my light? View >
  • Why are the shadows looking stripey and being cast in strange places? View >
  • Why do area lights take so long to render shadows? View >
  • Why does the occlusion pass or shadow pass not work when I plug it into the mask input? View >
  • How can I speed up rendering? View >

Caching

  • Why isn’t my cache working when I load it from disk? View >
  • Why does Post Light recalculate all the time when I set it to Cache mode? View >

Miscellaneous

  • Are you using the graphics card to accelerate the rendering? View >
  • What’s an octree? View >


Installation

  • Why can’t I find the Post Light plug-ins in the FXTree?
    • The XSI-Addon file does not automatically install the FXTree plug-ins. Please read the installation instructions.

Scene Preparation

  • Will Post Light work with any render tree that I use for my object materials?
    • No. Post Light only works with a Phong lighting model. While other illumination models provide a similar look (e.g. Blinn), you’ll find it very hard to produce passes for Post Light that will reproduce Mental Ray’s results accurately.
  • Will Post Light work with hair and particles?
    • No. Post Light only works with a Phong lighting model. Hair and particles tend to use quite a different shading model.
  • Will Post Light work with transparency and refractions?
    • In most cases, no. In order to render correctly, Post Light would need to have information about the entire ray history for each pixel. The only time transparency will work is if the surface is completely transparent, but you’ll have to know exactly what you’re doing with setting up the render passes in order for this to work correctly.
  • Will Post Light work with reflections?
    • No, not directly (for the same reason as transparency). But you can add them in using the Post Light Encode tool. See "Adding your own custom passes".

Passes

  • What passes do I need?
    • You need Color, Specular, Specular Roughness, Normal, and Position.
  • Is there an easy way to make the passes?
    • Yes! Use the PostLightPhong shader instead of XSI’s Phong shader. It has a single parameter that is easy to override in the passes and it will automatically produce the correct output.
  • Can I just use XSI’s standard (diffuse / specular / normal / etc.) pass?
    • The safest answer for me to give at this stage is "probably not". I haven’t had time to check out all the different passes produced by XSI yet, and until I have, it’s safest to use the PostLightPhong shader.
  • Why don’t my bumps show up in the normal pass?
    • You’ve probably got bump enabled in a shader that isn’t connected to a bump input. The PostLightPhong shader cannot output normals if you use this method. All bump must go through bump inputs, either on the PostLightPhong shader, or on the material.

Usage

  • Why do I need the Post Light Monitor?
    • The Post Light Monitor provides an automatic refresh for the Post Light tool every time you change the lighting in your scene. This method of using a Custom Display Host plugin is the only way that the plugin architecture of XSI supports detecting these scene change events.
  • Why do I need the Post Light Encode tool?
    • The Post Light Encode provides a way of getting your own passes into Post Light.
  • What’s the difference between the two inputs on the Post Light Encode tool?
    • One input is for diffuse lighting such as global illumination, and the other is for additive effects such as reflections and specular highlights.
  • I’m getting annoyed. Everytime I change a setting I have to wait for Post Light to re-render.
    • If you’re changing a light setting, then just turn off Auto-Refresh in the Post Light Monitor.
    • If you’re changing a setting inside Post Light’s PPG, then just close the FX Viewer, or alternatively, select a node to view that’s upstream of the Post Light tool.

Rendering

  • Why has Post Light rendered a black image?
    • Your light wildcard is incorrect. Try setting it to * to test it.
    • Your lights have their XSI visibility settings set to a configuration that doesn’t match Post Light’s light visibility settings.
    • You’ve got cache mode enabled in the Settings tab.
  • Why doesn’t Post Light react to my light?
    • Your light wildcard is incorrect. Try setting it to * to test it.
    • Your light has it’s XSI visibility settings set to a configuration that doesn’t match Post Light’s light visibility settings.
    • You don’t have the Post Light Monitor loaded in a Custom Display Host view.
  • Why are the shadows looking stripey and being cast in strange places?
    • You are probably using the actual objects themselves to cast shadows. You need to create copies and shrink them down slightly (try using the push deform operator). If you try to use the actual objects, they will self shadow themselves unpredictably.
  • Why do area lights take so long to render shadows?
    • Area lights can be thought of as an array of point lights. If you set your area light to use a sampling of U=6 and V=6, then effectively you’ve just added 36 lights to the scene. If you are casting shadows in an image of 720 x 576, then that makes nearly 15 million intersection tests for each shadow object. I’m sure you can now see why you need to keep your polygon count low for your shadow object!
  • Why does the occlusion pass or shadow pass not work when I plug it into the mask input?
    • Make sure that the input image has no Alpha channel as it will cause problems. If you’re using an Image Input node, just set the output type to RGB.
  • How can I speed up rendering?
            (Starting with the obvious suggestions:)

    • Use fewer lights.
    • Avoid area lights where possible.
    • Disable shadows.
    • Use as few polygons as possible in your proxy shadow casting objects.
    • Disable area light shadows.
    • Use Post Light’s caching system.

Caching

  • Why isn’t my cache working when I load it from disk?
    • Did you save the cache in a floating point format? E.g. Mental Ray Color Texture format
    • Check that the File Input node has its output bit depth set to "float"
  • Why does Post Light recalculate all the time when I set it to Cache mode?
    • You probably don’t have enough memory for the FX Tree to store the cache in memory. You’ll need to save it to disk in a floating point file format.

Miscellaneous

  • Are you using the graphics card to accelerate the rendering?
    • No, not yet. This may be an area for future research.
  • What’s an octree?
    • An octree is a way of improving the efficiency of detecting collisions between a ray and a polygon mesh. It splits up the polygon mesh into smaller chunks by recursively subdividing the bounding box into 8 smaller regions on each subdivision. It only subdivides when the number of polygons in that region exceed a specified threshold.
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3 Comments »

  • Adam Seeley said:

    Hi, Any idea if this works in Xp 64 bit Soft 2010/2011/2011 sp1.

    Thanks,

    Adam.

  • AndyN (author) said:

    Hi Adam,
    That’s a good question. I can’t see a reason why not, but it would need to be recompiled and I’m afraid I don’t have access to a Windows 64bit machine.

    It could only support phong based lighting models so it didn’t catch on as it probably wasn’t flexible enough for most pipelines. Anyway, as a result, I haven’t kept it up to date.

    Sorry!

  • Moykul said:

    Brilliant tool! Thank you so much!

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