An example of image-based lighting in stack.gl.
Shade adapted from "OpenGL Shading Language", third edition (the Orange Book).
HDR image source: http://www.hdrv.org/Resources.php (used under the terms of the creative commons license CC BY-NC 3.0).
Here is the process used to generate the cube maps from this HDR source. Note that most "free as beer" tools are aging or unmaintened as of 2016.
- The original "exr" file was resized to 128x64 (Mitchell filter, with default 0.64 sharpness) and converted to "hdr" file format using Picturenaut 3.2.
- Diffuse and specular lat-long maps were convoluted using HDRShop 1.0 (Image > Panorama > Diffuse/Specular Convolution), with "1" and "50" Phong exponent respectively.
- "Vertical cross" cubemaps were generated from convoluted maps using HDRShop 1.0 (Image > Panorama > Panoramic Transformations).
- Tone mapping was performed by Picturenaut, with default values, 8 bits output; the resulting ("low dynamic range") files were saved to jpeg with a quality of 70. Note: seems like the default "bilinear" algorithm produce washed-out images; "exposure" seems easier to control.
- The vertical cross cubemaps to 6 images conversions was performed by ATI's CubeMapGen:
- "Load Cube Cross",
- "Export Image Layout: OpenGL Cube",
- "Edge Fixup": width=2,
- "Filter Cubemap",
- "Save CubeMap to Images"
A test image from Horde3D
was used to check ATI's CubeMapGen images numbering: _c00 to _c05 are hence PX, NX, PY, NY, PZ, NZ.