2020-10-29 03:39:34 +00:00
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# Translations
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This document attempts to document how WGSL translates into the various backends
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for the cases where the translation is not a direct mapping.
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# Access Control
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## HLSL
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* ReadOnly -> `ByteAddressBuffer`
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* ReadWrite -> `RWByteAddressBuffer`
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## MSL
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* ReadOnly -> `const`
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## SPIR-V
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There are two ways this can be achieved in SPIR-V. Either the variable can be
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decorated with `NonWritable` or each member of the struct can be decorated with
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`NonWritable`. We chose to go the struct member route.
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* The read-only becomes part of the type in this case. Otherwise, you are
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treating the readonly type information as part of the variable which is
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confusing.
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* Treating the readonly as part of the variable means we should be
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deduplicating the types behind the access control, which causes confusing
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with the type_names and various tracking systems within Tint.
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# Builtin Decorations
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2020-10-29 12:44:32 +00:00
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| Name | SPIR-V | MSL | HLSL |
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|------|--------|-----|------|
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| position | SpvBuiltInPosition |position | SV_Position |
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| vertex_idx | SpvBuiltInVertexIndex |vertex_id | SV_VertexID |
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| instance_idx | SpvBuiltInInstanceIndex | instance_id| SV_InstanceID |
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| front_facing | SpvBuiltInFrontFacing | front_facing | SV_IsFrontFacing |
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| frag_coord | SpvBuiltInFragCoord | position | SV_Position |
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| frag_depth | SpvBuiltInFragDepth | depth(any) | SV_Depth |
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| local_invocation_id | SpvBuiltInLocalInvocationId | thread_position_in_threadgroup | SV_GroupThreadID |
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| local_invocation_idx | SpvBuiltInLocalInvocationIndex | thread_index_in_threadgroup | SV_GroupIndex |
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| global_invocation_id | SpvBuiltInGlobalInvocationId | thread_position_in_grid | SV_DispatchThreadID |
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2020-10-29 03:39:34 +00:00
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# Builtins Methods
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2020-10-29 12:44:32 +00:00
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| Name | SPIR-V | MSL | HLSL |
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| ------|--------|-----|------ |
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| abs | GLSLstd450FAbs or GLSLstd450SAbs| fabs or abs | abs |
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| acos | GLSLstd450Acos | acos | acos |
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| all | SpvOpAll | all | all |
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| any | SpvOpAny | any | any |
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| arrayLength | SpvOpArrayLength | | |
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| asin | GLSLstd450Asin | asin | asin |
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| atan | GLSLstd450Atan | atan | atan |
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| atan2 | GLSLstd450Atan2| atan2 | atan2 |
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| ceil | GLSLstd450Ceil| ceil | ceil |
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| clamp | GLSLstd450NClamp or GLSLstd450UClamp or GLSLstd450SClamp| clamp | clamp |
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| cos | GLSLstd450Cos | cos | cos |
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| cosh | GLSLstd450Cosh | cosh | cosh |
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| countOneBits | SpvOpBitCount | popcount | countbits |
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| cross | GLSLstd450Cross | cross | cross |
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| determinant | GLSLstd450Determinant | determinant | determinant |
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| distance | GLSLstd450Distance | distance | distance |
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| dot | SpOpDot | dot | dot |
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| dpdx | SpvOpDPdx | dpdx | ddx |
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| dpdxCoarse | SpvOpDPdxCoarse | dpdx | ddx_coarse |
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| dpdxFine | SpvOpDPdxFine | dpdx | ddx_fine |
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| dpdy | SpvOpDPdy | dpdy | ddy |
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| dpdyCoarse | SpvOpDPdyCoarse | dpdy | ddy_coarse |
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| dpdyFine | SpvOpDPdyFine | dpdy | ddy_fine |
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| exp | GLSLstd450Exp | exp | exp |
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| exp2 | GLSLstd450Exp2 | exp2 | exp2 |
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| faceForward | GLSLstd450FaceForward | faceforward | faceforward |
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| floor | GLSLstd450Floor | floor | floor |
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| fma | GLSLstd450Fma | fma | fma |
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| fract | GLSLstd450Fract | fract | frac |
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| frexp | GLSLstd450Frexp | | |
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| fwidth | SpvOpFwidth | fwidth | fwidth |
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| fwidthCoarse | SpvOpFwidthCoarse | fwidth | fwidth |
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| fwidthFine | SpvOpFwidthFine | fwidth | fwidth |
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| inverseSqrt | GLSLstd450InverseSqrt | rsqrt | rsqrt |
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| isFinite | | isfinite | isfinite |
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| isInf | SpvOpIsInf | isinf | isinf |
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| isNan | SpvOpIsNan | isnan | isnan |
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| isNormal | | isnormal | |
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| ldexp | GLSLstd450Ldexp | | |
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| length | GLSLstd450Length | length | length |
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| log | GLSLstd450Log | log | log |
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| log2 | GLSLstd450Log2 | log2 | log2 |
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| max | GLSLstd450NMax or GLSLstd450SMax or GLSLstd450UMax | fmax or max | max |
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| min | GLSLstd450NMin or GLSLstd450SMin or GLSLstd450UMin | fmin or min | min |
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| mix | GLSLstd450FMix | mix | mix |
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| modf | GLSLstd450Modf | | |
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| normalize | GLSLstd450Normalize | normalize | normalize |
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| outerProduct | SpvOpOuterProduct | | |
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| pow | GLSLstd450Pow | pow | pow |
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| reflect | GLSLstd450Reflect | reflect | reflect |
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| reverseBits | SpvOpBitReverse | reverse_bits | reversebits |
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| round | GLSLstd450Round | round | round |
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| select | SpvOpSelect | select | |
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| sign | GLSLstd450FSign | sign | sign |
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| sin | GLSLstd450Sin | sin | sin |
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| sinh | GLSLstd450Sinh | sinh | sinh |
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| smoothStep | GLSLstd450SmoothStep | smoothstep | smoothstep |
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| sqrt | GLSLstd450Sqrt | sqrt | sqrt |
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| step | GLSLstd450Step | step | step |
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| tan | GLSLstd450Tan | tan | tan |
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| tanh | GLSLstd450Tanh | tanh | tanh |
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| trunc | GLSLstd450Trunc | trunc | trunc |
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2020-10-29 03:39:34 +00:00
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# Short-circuting
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## HLSL
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TODO(dsinclair): Nested if's
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## SPIR-V
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TODO(dsinclair): Nested if's
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# Storage classes
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TODO(dsinclair): do ...
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# Storage buffers
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## HLSL
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TODO(dsinclair): Rewriting of accessors to loads
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# Loop blocks
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## HLSL
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TODO(dsinclair): Rewrite with bools
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## MSL
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TODO(dsinclair): Rewrite with bools
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# Input / Output storage class
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## HLSL
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TODO(dsinclair): Structs and params
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## MSL
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TODO(dsinclair): Structs and params
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# Discard
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## HLSL
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* `discard`
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## MSL
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* `discard_fragment()`
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# Specialization constants
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## HLSL
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```
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#ifndef WGSL_SPEC_CONSTANT_<id>
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-- if default provided
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#define WGSL_SPEC_CONSTANT_<id> default value
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-- else
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#error spec constant required for constant id
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--
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#endif
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static const <type> <name> = WGSL_SPEC_CONSTANT_<id>
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```
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## MSL
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`[[function_constant(<id>)]]`
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