How about making a dword:

Assign each shader option the required amount of bits ie. for each Y/N fields 1 bit, num dir lights 2 bits, point lights 3 bits etc. Then calculate the total amount of bits you need.

Then you may create a loop:

HLSL_DEFINES MyDefines;

for(dword i = 0; i < 2^Numbits; ++i)

{

DecodeShaderPermutation(i, MyDefines); //decode bits fields from the loop counter value and update the HLSL_DEFINES based on the value

Compile(...); // profit

}

The loop counter will produce all the combinations required.

Cheers!

How about making a dword:

Assign each shader option the required amount of bits ie. for each Y/N fields 1 bit, num dir lights 2 bits, point lights 3 bits etc. Then calculate the total amount of bits you need.

Then you may create a loop:

HLSL_DEFINES MyDefines;

for(dword i = 0; i < 2^Numbits; ++i)

{

DecodeShaderPermutation(i, MyDefines); //decode bits fields from the loop counter value and update the HLSL_DEFINES based on the value

Compile(...); // profit

}

The loop counter will produce all the combinations required.

Cheers!

I've done this at work, and it was quite successful. One added benefit is that by encoding permutations inside a dword you have a very easy way to name and refer to specific permutations. What might be called "uber_shader" out in your tools becomes a bunch of "uber_shader_XXXXXXXX" after the permutations have been compiled, where XXXXXXXX is the permutation index. Then when you want to select a shader, your material can contain a set of permutation bits (use normal map, use specular, etc), and the runtime game can provide the remaining bits (n point lights, 1 direction light), which get OR'ed together resulting in a full dword which can be used to quickly look up the shader you need to select.

Well it requires some bitwork, ie. shifting and masking. First of all, you'll need to decide yourself the layout of the bits such as

bit 0 : Ambient fog (one bit is enough for yes/no)

bit 1 : Normal map

bit 2-3 : Num Point lights (2 bits is enough for values between 0-3)

bit ...

As the loop counter presents all the shader permutations, only thing left is to extract each bit field (variable "i" is the loop counter presented in the earlier post):

bool AmbientFog = i & 1; (the desired value is in the first bit so masking out other bits is enough)

bool NormalMap = (i >> 1) & 1; (the desired value is in the second bit so one shift is necessary and masking after)

int NumPointLights = (i >> 2) & 3;

...

4 bits are used here (you'll need few bits more) so the loop needs to be run 2^4 times.

Shifts are practically multiplies / divisions by 2^(shift value) which effectively will move the bits in the desired positions. After shifting is is necessary to use AND (&) operator to mask out unwanted bits.

The loop creating all the permutations doesn't know about the required usage - ie. it can't know whether a permutation is used or not. Nothing prevents you from creating permutations while program is running (and saving them to disk in order to accelerate the program operation). Of course this maybe produce slowdowns if a new shader permuation is required.

Cheers!

Well it requires some bitwork, ie. shifting and masking. First of all, you'll need to decide yourself the layout of the bits such as

bit 0 : Ambient fog (one bit is enough for yes/no)

bit 1 : Normal map

bit 2-3 : Num Point lights (2 bits is enough for values between 0-3)

bit ...

As the loop counter presents all the shader permutations, only thing left is to extract each bit field (variable "i" is the loop counter presented in the earlier post):

bool AmbientFog = i & 1; (the desired value is in the first bit so masking out other bits is enough)

bool NormalMap = (i >> 1) & 1; (the desired value is in the second bit so one shift is necessary and masking after)

int NumPointLights = (i >> 2) & 3;

...

4 bits are used here (you'll need few bits more) so the loop needs to be run 2^4 times.

Shifts are practically multiplies / divisions by 2^(shift value) which effectively will move the bits in the desired positions. After shifting is is necessary to use AND (&) operator to mask out unwanted bits.

The loop creating all the permutations doesn't know about the required usage - ie. it can't know whether a permutation is used or not. Nothing prevents you from creating permutations while program is running (and saving them to disk in order to accelerate the program operation). Of course this maybe produce slowdowns if a new shader permuation is required.

Cheers!

Do i understand this approach correctly: You compile all the shader permutations in runtime (at startup for example)?

Is it possible to compile the shader permutations in build time, but still having the luxury of having them named nicely, so they can be identified at runtime by using the bitmask you suggested above?