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August 2003 Efficient High-Level Shader Development Natalya Tatarchuk 3D Application Research Group ATI Technologies, Inc.

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Presentation on theme: "August 2003 Efficient High-Level Shader Development Natalya Tatarchuk 3D Application Research Group ATI Technologies, Inc."— Presentation transcript:

1 August 2003 Efficient High-Level Shader Development Natalya Tatarchuk 3D Application Research Group ATI Technologies, Inc.

2 August 2003 Overview Writing optimal HLSL code –Compiling issues –Optimization strategies –Code structure pointers HLSL Shader Examples –Multi-layer car paint effect –Translucent Iridescent Shader –Überlight Shader

3 August 2003 Why use HLSL? Faster, easier effect development –Instant readability of your shader code –Better code re-use and maintainability –Optimization Added benefit of HLSL compiler optimizations Still helps to know whats under the hood Industry standard which will run on cards from any vendor –Current and future industry direction Increase your ability to iterate on a given shader design, resulting in better looking games Conveniently manage shader permutations

4 August 2003 Compile Targets Legal HLSL is still independent of compile target chosen But having an HLSL shader doesnt mean it will always run on any hardware! Currently supported compile targets: –vs_1_1, vs_2_0, vs_2_sw –ps_1_1, ps_1_2, ps_1_3, ps_1_4, ps_2_0, ps_2_sw Compilation is vendor-independent and is done by a D3DX component that Microsoft can update independent of the runtime release schedule

5 August 2003 Compilation Failure The obvious: program errors (bad syntax, etc) Compile target specific reasons – your shader is too complex for the selected target –Not enough resources in the selected target Uses too many registers (temporaries, for example) Too many resulting asm instructions for the compile target –Lack of capability in the target Such as trying to sample a texture in vs_1_1 Using dynamic branching when unsupported in the target Sampling texture too many times for the target (Example: more than 6 for ps_1_4) Compiler provides useful messages

6 August 2003 Use Disassembly for Hints Very helpful for understanding relationship between compile targets and code generation Disassembly output provides valuable hints when compiling down to an older compile target If successfully compiled for a more recent target (eg. ps_2_0), look at the disassembly output for hints when failing to compile to an older target (eg. ps_1_4) –Check out instruction count for ALU and tex ops –Figure out how HLSL instructions get mapped to assembly

7 August 2003 Getting Disassembly Output for Your Shaders Directly use FXC –Compile for any target desired –Compile both individual shader files and full effects –Various input arguments Allow to turn shader optimizations on / off Specify different entry points Enable / disable generating debug information

8 August 2003 Easier Path to Disassembly Use RenderMonkey while developing shaders –See your changes in real-time Disassembly output is updated every time a shader is compiled –Displays count for ALU and texture ops, as well as the limits for the selected target –Can save resulting assembly code into text file

9 August 2003 Optimizing HLSL Shaders Dont forget you are running on a vector processor Do your computations at the most efficient frequency –Dont do something per-pixel that you can do per-vertex –Dont perform computation in a shader that you can precompute in the app Use HLSL intrinsic functions –Helps hardware to optimize your shaders –Know your intrinsics and how they map to asm, especially asm modifiers

10 August 2003 HLSL Syntax Not Limited The HLSL code you write is not limited by the compile target you choose You can always use loops, subroutines, if-else statements etc If not natively supported in the selected compile target, the compiler will still try to generate code: –Loops will be unrolled –Subroutines will be inlined –If – else statements will execute both branches, selecting appropriate output as the result Code generation is dependent upon compile target Use appropriate data types to improve instruction count –Store your data in a vector when needed –However, using appropriate data types helps compiler do better job at optimizing your code

11 August 2003 Using If Statement in HLSL Can have large performance implications –Lack of branching support in most asm models –Both sides of an if statement will be executed –The output is chosen based on which side of the if would have been taken Optimization is different than in the CPU programming world

12 August 2003 Example of Using If in Vs_1_1 If ( Threshold > 0.0 ) Out.Position = Value1; else Out.Position = Value2; // calculate lerp value based on Value > 0 mov r1.w, c2.x slt r0.w, c3.x, r1.w // lerp between Value1 and Value2 mov r7, -c1 add r2, r7, c0 mad oPos, r0.w, r2, c1 generates following assembly output:

13 August 2003 Example of Function Inlining // Bias and double a value to take it from 0..1 range to -1..1 range float4 bx2 (float x) { return 2.0f * x - 1.0f; } float4 main( float4 tc0 : TEXCOORD0, float4 tc1 : TEXCOORD1, float4 tc2 : TEXCOORD2, float4 tc3 : TEXCOORD3) : COLOR { // Sample noise map three times with different // texture coordinates float4 noise0 = tex2D(fire_distortion, tc1); float4 noise1 = tex2D(fire_distortion, tc2); float4 noise2 = tex2D(fire_distortion, tc3); // Weighted sum of signed noise float4 noiseSum = bx2 (noise0) * distortion_amount0 + bx2 (noise1) * distortion_amount1 + bx2 (noise2) * distortion_amount2; // Perturb base coordinates in direction of noiseSum as function of height (y) float4 perturbedBaseCoords = tc0 + noiseSum * (tc0.y * height_attenuation.x + height_attenuation.y); // Sample base and opacity maps with perturbed coordinates float4 base = tex2D(fire_base, perturbedBaseCoords); float4 opacity = tex2D(fire_opacity, perturbedBaseCoords); return base * opacity; }

14 August 2003 Code Permutations Via Compilation static const bool bAnimate = false; VS_OUTPUT vs_main( float4 Pos: POSITION, float2 Tex: TEXCOORD0 ) { VS_OUTPUT Out = (VS_OUTPUT) 0; Out.Pos = mul( view_proj_matrix, Pos ); if ( bAnimate ) { Out.Tex.x = Tex.x + time / 2; Out.Tex.y = Tex.y - time / 2; } else Out.Tex = Tex; return Out; } bool bAnimate = false; VS_OUTPUT vs_main( float4 Pos: POSITION, float2 Tex: TEXCOORD0 ) { VS_OUTPUT Out = (VS_OUTPUT) 0; Out.Pos = mul( view_proj_matrix, Pos ); if ( bAnimate ) { Out.Tex.x = Tex.x + time / 2; Out.Tex.y = Tex.y - time / 2; } else Out.Tex = Tex; return Out; } static const bool bAnimate = false;vs_1_1 dcl_position v0 dcl_texcoord v1 mul r0, v0.y, c1 mad r0, c0, v0.x, r0 mad r0, c2, v0.z, r0 mad oPos, c3, v0.w, r0 mov oT0.xy, v1 5 instructions vs_1_1 def c6, 0.5, 0, 0, 0 dcl_position v0 dcl_texcoord v1 mul r0, v0.y, c1 mad r0, c0, v0.x, r0 mov r1.w, c4.x mul r1.x, r1.w, c6.x mad r0, c2, v0.z, r0 mov r1.y, -r1.x mad oPos, c3, v0.w, r0 mad oT0.xy, c5.x, r1, v1 8 instructions const bool bAnimate = false;

15 August 2003 Scalar and Vector Data Types Scalar data types are not all natively supported in hardware –i.e. integers are emulated on float hardware Not all targets have native half and none currently have double Can apply swizzles to vector types float2 vec = pos.xy –But! Not all targets have fully flexible swizzles Acquaint yourself with the swizzles native to the relevant compile targets (particularly ps_2_0 and lower)

16 August 2003 Integer Data Type Added to make relative addressing more efficient Using floats for addressing purposes without defined truncation rules can result in incorrect access to arrays. All inputs used as ints should be defined as ints in your shader

17 August 2003 Example of Integer Data Type Usage Matrix palette indices for skinning –Declaring variable as an int is a free operation => no truncation occurs –Using a float and casting it to an int or using directly => truncation will happen Out.Position = mul( inPos, World[Index]); // Index declared as float frc r0.w, r1.w add r2.w, -r0.w, r1.w mul r9.w, r2.w, c61.x mova a0.x, r9.w m4x4 oPos, v0, c0[a0.x] // Index declared as int mul r0.w, c60.x, r1.w mova a0.x, r0.w m4x4 oPos, v0, c0[a0.x] Code generated with float index vs integer index

18 August 2003 Real-World Shader Examples Will present several case studies of developing shaders used in ATIs demos –Multi-tone car paint effect –Translucent iridescent effect –Classic ü berlight example Examples are presented as RenderMonkey TM workspaces –Distributed publicly with version 1.0 release

19 August 2003 Multi-Tone Car Paint

20 August 2003 Multi-Tone Car Paint Effect Multi-tone base color layer Microflake layer simulation Clear gloss coat Dynamically Blurred Reflections

21 August 2003 Car Paint Layers Build Up Multi-Tone Base Color Microflake Layer Clear gloss coatFinal Color Composite

22 August 2003 Multi-Tone Base Paint Layer View-dependent lerping between three paint colors Normal from appearance preserving simplification process, N Uses subtractive tone to control overall color accumulation

23 August 2003 Normal Decompression Sample from two-channel 16-16 normal map Derive z from +sqrt (1 – x 2 – y 2 ) Gives higher precision than typically used 8-8-8-8 normal map

24 August 2003 Multi-Tone Base Coat Vertex Shader VS_OUTPUT main( float4 Pos : POSITION, float3 Normal : NORMAL, float2 Tex : TEXCOORD0, float3 Tangent : TANGENT, float3 Binormal: BINORMAL ) { VS_OUTPUT Out = (VS_OUTPUT) 0; // Propagate transformed position out: Out.Pos = mul( view_proj_matrix, Pos ); // Compute view vector: Out.View = normalize( mul(inv_view_matrix, float4( 0, 0, 0, 1)) - Pos ); // Propagate texture coordinates: Out.Tex = Tex; // Propagate tangent, binormal, and normal vectors to pixel shader: Out.Normal = Normal; Out.Tangent = Tangent; Out.Binormal = Binormal; return Out; }

25 August 2003 Multi-Tone Base Coat Pixel Shader float4 main( float4 Diff: COLOR0, float2 Tex: TEXCOORD0, float3 Tangent: TEXCOORD1, float3 Binormal: TEXCOORD2, float3 Normal: TEXCOORD3, float3 View: TEXCOORD4 ) : COLOR { float3 vNormal = tex2D( normalMap, Tex ); vNormal = 2 * vNormal - 1.0; float3 vView = normalize( View ); float3x3 mTangentToWorld = transpose( float3x3( Tangent, Binormal, Normal )); float3 vNormalWorld = normalize( mul(mTangentToWorld,vNormal)); float fNdotV = saturate( dot( vNormalWorld, vView ) ); float fNdotVSq = fNdotV * fNdotV; float4 paintColor = fNdotV * paintColor0 + fNdotVSq * paintColorMid + fNdotVSq * fNdotVSq * paintColor2; return float4( paintColor.rgb, 1.0 ); } Compute the result color by lerping three input tones using computed fresnel term. Fetch normal from a normal map and scale and bias it to move into [-1; 1] Compute Nw V using world-space normal vector Normalize the view vector to ensure higher quality results

26 August 2003 Microflake Layer

27 August 2003 Microflake Deposit Layer Simulating light interaction resulting from metallic flakes suspended in the enamel coat of the paint Uses high frequency normalized vector noise map (Nn) which is repeated across the surface of the car

28 August 2003 Computing Microflake Layer Normals Start out by using normal vector fetched from the normal map, N Using the high frequency noise map, compute perturbed normal N p Simulate two layers of microflake deposits by computing perturbed normals N p1 and N p2 where a << b where c = b

29 August 2003 Microflake Layer Vertex Shader VS_OUTPUT main(float4 Pos: POSITION, float3 Normal: NORMAL, float2 Tex: TEXCOORD0, float3 Tangent: TANGENT, float3 Binormal: BINORMAL ) { VS_OUTPUT Out = (VS_OUTPUT) 0; // Propagate transformed position out: Out.Pos = mul( view_proj_matrix, Pos ); // Compute view vector: Out.View = normalize(mul(inv_view_matrix, float4(0, 0, 0, 1))- Pos); // Propagate texture coordinates: Out.Tex = Tex; // Propagate tangent, binormal, and normal vectors to pixel // shader: Out.Normal = Normal; Out.Tangent = Tangent; Out.Binormal = Binormal; // Compute microflake tiling factor: Out.SparkleTex = float4( Tex * fFlakeTilingFactor, 0, 1 ); return Out; } Compute texture coordinates for accessing noise map using input texture coordinates and a tiling factor

30 August 2003 Microflake Layer Pixel Shader float4 main(float4 Diff: COLOR0, float2 Tex : TEXCOORD0, float3 Tangent: TEXCOORD1, float3 Binormal: TEXCOORD2, float3 Normal: TEXCOORD3, float3 View: TEXCOORD4, float3 SparkleTex : TEXCOORD5 ) : COLOR { … fetch and signed scale the normal fetched from the normal map float3 vFlakesNormal = 2 * tex2D( microflakeNMap, SparkleTex ) - 1; float3 vNp1 = microflakePerturbationA * vFlakesNormal + normalPerturbation * vNormal ; float3 vNp2 = microflakePerturbation * ( vFlakesNormal + vNormal ) ; float3 vView = normalize( View ); float3x3 mTangentToWorld = transpose( float3x3( Tangent, Binormal, Normal )); float3 vNp1World = normalize( mul( mTangentToWorld, vNp1) ); float fFresnel1 = saturate( dot( vNp1World, vView )); float3 vNp2World = normalize( mul( mTangentToWorld, vNp2 )); float fFresnel2 = saturate( dot( vNp2World, vView )); float fFresnel1Sq = fFresnel1 * fFresnel1; float4 paintColor = fFresnel1 * flakeColor + fFresnel1Sq * flakeColor + fFresnel1Sq * fFresnel1Sq * flakeColor + pow( fFresnel2, 16 ) * flakeColor; return float4( paintColor, 1.0 ); } Fetch initial perturbed normal vector from the noise map Compute dot products of the normalized view vector with the two microflaker layer normals Compose the microflake layer color Compute normal vectors for both microflake layers

31 August 2003 Clear Gloss Coat

32 August 2003 RGBScale HDR Environment Map Alpha channel contains 1 / 16 of the true HDR scale of the pixel value RGB contains normalized color of the pixel Pixel shader reconstructs HDR value from scale*8*color to get half of the true HDR value Obvious quantization issues, but reasonable for some applications Similar to Wards RGBE Real Pixels but simpler to reconstruct in the pixel shader

33 August 2003 Environment Map Top Cube Map Face RGB Top Face Scale in Alpha Channel Ceiling of car showroom

34 August 2003 Dynamically Blurred Reflections Blurred Reflections

35 August 2003 Dynamic Blurring of Environment Map Reflections A gloss map can be supplied to specify the regions where reflections can be blurred Use bias when sampling the environment map to vary blurriness of the resulting reflections Use texCUBEbias for to access the cubic environment map For rough specular, the bias is high, causing a blurring effect Can also convert color fetched from environment map to luminance in rough trim areas

36 August 2003 Clear Gloss Coat Pixel Shader float4 ps_main(... /* same inputs as in the previous shader */ ) { //... use normal in world space (see Multi-tone pixel shader) // Compute reflection vector: float fFresnel = saturate(dot( vNormalWorld, vView)); float3 vReflection = 2 * vNormalWorld * fFresnel - vView; float fEnvBias = glossLevel; // Sample environment map using this reflection vector and bias: float4 envMap = texCUBEbias( showroomMap, float4( vReflection, fEnvBias ) ); // Premultiply by alpha: envMap.rgb = envMap.rgb * envMap.a; // Brighten the environment map sampling result: envMap.rgb *= brightnessFactor; // Combine result of environment map reflection with the paint // color: float fEnvContribution = 1.0 - 0.5 * fFresnel; return float4( envMap.rgb * fEnvContribution, 1.0 ); } Premultiply by alpha channel of the environment map to avoid clamping highlights and brighten the reflections Resulting reflective highlights Shader parameter is used to dynamically blur the reflections by biasing the texture fetch from the environment map Compute the reflection vector to fetch from the environment map

37 August 2003 Compositing Multi-Tone Base Layer and Microflake Layer Base color and flake effect are derived from N p1 and N p2 using the following polynomial: color 0 (N p1 ·V) + color 1 (N p1 ·V) 2 + color 2 (N p1 ·V) 4 + color 3 (N p2 ·V) 16 Base ColorFlake

38 August 2003 Compositing Final Look {... // Compute final paint color: combines all layers of paint as well // as two layers of microflakes: float fFresnel1Sq = fFresnel1 * fFresnel1; float4 paintColor = fFresnel1 * paintColor0 + fFresnel1Sq * paintColorMid + fFresnel1Sq * fFresnel1Sq * paintColor2 + pow( fFresnel2, 16 ) * flakeLayerColor; // Combine result of environment map reflection with the paint // color: float fEnvContribution = 1.0 - 0.5 * fNdotV; // Assemble the final look: float4 finalColor; finalColor.a = 1.0; finalColor.rgb = envMap * fEnvContribution + paintColor; return finalColor; }

39 August 2003 Original Hand-Tuned Assembly ps.2.0 def c0, 0.0, 0.5, 1.0, 2.0 def c1, 0.0, 0.0, 1.0, 0.0 dcl_2d s0 dcl_2d s1 dcl_cube s2 dcl_2d s3 dcl t0 dcl t1 dcl t2 dcl t3 dcl t4 dcl t5 texld r0, t0, s1 texld r8, t5, s3 mad r3, r8, c0.w, -c0.z mad r6, r3, c4.r, r0 mad r7, r3, c4.g, r0 dp3 r4.a, t4, t4 rsq r4.a, r4.a mul r4, t4, r4.a mul r2.rgb, r0.x, t1 mad r2.rgb, r0.y, t2, r2 mad r2.rgb, r0.z, t3, r2 dp3 r2.a, r2, r2 rsq r2.a, r2.a mul r2.rgb, r2, r2.a dp3_sat r2.a, r2, r4 mul r3, r2, c0.w... mad r1.rgb, r2.a, r3, -r4 mov r1.a, c10.a texldb r0, r1, s2 mul r10.rgb, r6.x, t1 mad r10.rgb, r6.y, t2, r10 mad r10.rgb, r6.z, t3, r10 dp3 r10.a, r10, r10 rsq r10.a, r10.a mul r10.rgb, r10, r10.a dp3_sat r6.a, r10, r4 mul r10.rgb, r7.x, t1 mad r10.rgb, r7.y, t2, r2 mad r10.rgb, r7.z, t3, r2 dp3 r10.a, r10, r10 rsq r10.a, r10.a mul r10.rgb, r10, r10.a dp3_sat r7.a, r10, r4 mul r0.rgb, r0, r0.a mul r0.rgb, r0, c2.r mov r4.a, r6.a mul r4.rgb, r4.a, c5 mul r4.a, r4.a, r4.a mad r4.rgb, r4.a, c6, r4 mul r4.a, r4.a, r4.a mad r4.rgb, r4.a, c7, r4 pow r4.a, r7.a, c4.b mad r4.rgb, r4.a, c8, r4 mad r1.a, r2.a, c2.z, c2.w mad r6.rgb, r0, r1.a, r4 mov oC0, r6 40 ALU ops 3 Tex Fetches 43 Total

40 August 2003 Car Paint Shader HLSL Compiler Disassembly Output ps_2_0 def c9, 0.5, 1, 0, 0 def c10, 2, -1, 16, 1 dcl t0.xy dcl t1.xyz dcl t2.xyz dcl t3.xyz dcl t4.xyz dcl t5.xy dcl_2d s0 dcl_2d s1 dcl_cube s2 texld r0, t0, s1 mad r5.xyz, c10.x, r0, c10.y mul r0.xyz, r5.y, t2 dp3 r1.x, t4, t4 mad r0.xyz, t1, r5.x, r0 rsq r0.w, r1.x mad r1.xyz, t3, r5.z, r0 mul r3.xyz, r0.w, t4 nrm r0.xyz, r1 dp3_sat r6.x, r0, r3 mul r0.xyz, r0, r6.x add r0.xyz, r0, r0 mad r0.xyz, t4, -r0.w, r0 mov r0.w, c8.x texld r1, t5, s0 texldb r0, r0, s2 mad r2.xyz, c10.x, r1, c10.y mul r1.xyz, r5, c2.x mad r1.xyz, c3.x, r2, r1 mul r4.xyz, r1.y, t2 mad r4.xyz, t1, r1.x, r4 add r2.xyz, r5, r2 mad r4.xyz, t3, r1.z, r4 nrm r1.xyz, r4 mul r2.xyz, r2, c7.x dp3_sat r5.x, r1, r3 mul r1.xyz, r2.y, t2 mul r1.w, r5.x, r5.x mad r4.xyz, t1, r2.x, r1 mul r1.xyz, r1.w, c6 mad r4.xyz, t3, r2.z, r4 mul r1.w, r1.w, r1.w nrm r2.xyz, r4 mad r1.xyz, r5.x, c4, r1 dp3_sat r2.x, r2, r3 mad r1.xyz, r1.w, c5, r1 pow r1.w, r2.x, c10.z mad r1.xyz, r1.w, c1, r1 mul r0.xyz, r0.w, r0 mad r0.w, r6.x, -c9.x, c9.y mul r0.xyz, r0, c0.x mad r0.xyz, r0, r0.w, r1 mov r0.w, c10.w mov oC0, r0 38 ALU ops 3 Tex Fetches 41 Total !

41 August 2003 Full Result of Multi-Layer Paint

42 August 2003 Translucent Iridescent Shader: Butterfly Wings

43 August 2003 Translucent Iridescent Shader: Butterfly Wings Simulates translucency of delicate butterfly wings –Wings glow from scattered reflected light –Similar to the effect of softly backlit rice paper Displays subtle iridescent lighting –Similar to rainbow pattern on the surface of soap bubbles –Caused by the interference of light waves resulting from multiple reflections of light off of surfaces of varying thickness Combines gloss, opacity and normal maps for a multi-layered final look –Gloss map contributes to satiny highlights –Opacity map allows portions of wings to be transparent –Normal map is used to give wings a bump-mapped look

44 August 2003 RenderMonkey Butterfly Wings Shader Example Parameters that contribute to the translucency and iridescence look: –Light position and scene ambient color –Translucency coefficient –Gloss scale and bias –Scale and bias for speed of iridescence change Workspace: Iridescent Butterfly.rfx

45 August 2003 Translucent Iridescent Shader: Vertex Shader.. // Propagate input texture coordinates: Out.Tex = Tex; // Define tangent space matrix: float3x3 mTangentSpace; mTangentSpace[0] = Tangent; mTangentSpace[1] = Binormal; mTangentSpace[2] = Normal; // Compute the light vector (object space): float3 vLight = normalize( mul( inv_view_matrix, lightPos ) - Pos ); // Output light vector in tangent space: Out.Light = mul( mTangentSpace, vLight ); // Compute the view vector (object space): float3 vView = normalize( mul( inv_view_matrix, float4(0,0,0,1)) - Pos ); // Output view vector in tangent space: Out.View = mul( mTangentSpace, vView ); // Compute the half angle vector (in tangent space): Out.Half = mul( mTangentSpace, normalize( vView + vLight ) ); return Out; Compute Halfway vector H = V + L in tangent space Compute view vector in tangent space Compute light vector in tangent space Define tangent space matrix

46 August 2003 Translucent Iridescent Shader: Loading Information float3 vNormal, baseColor; float fGloss, fTranslucency; // Load normal and gloss map: float4( vNormal, fGloss ) = tex2D( bump_glossMap, Tex ); // Load base and opacity map: float4 (baseColor, fTranslucency) = tex2D( base_opacityMap, Tex ); Load base texture color and alpha value from combined base and opacity texture map Load normal from a normal map and gloss value from a gloss map (combined in one texture map)

47 August 2003 Diffuse Illumination For Translucency float3 scatteredIllumination = saturate(dot(-vNormal, Light)) * fTranslucency * translucencyCoeff; float3 diffuseContribution = saturate(dot(vNormal,Light)) + ambient; baseColor *= scatteredIllumination + diffuseContribution; Light scattered on the butterfly wings is computed based on the negative normal (for scattering off the surface), light vector and translucency coefficient and value for the given pixel. Compute diffusely reflected light using the bump-mapped normal and ambient contribution Combine diffuse and scattered light with base texture *( + ) =

48 August 2003 Adding Opacity to Butterly Wings Resulted color is modulated by the opacity value to add transparency to the wings: // Premultiply alpha blend to avoid clamping the highlights: baseColor *= fOpacity; * =

49 August 2003 Making Butterfly Wings Iridescent // Compute index into the iridescence gradient map, which // consists of N*V coefficient float fGradientIndex = dot( vNormal, View) * iridescence_speed_scale + iridescence_speed_bias; // Load the iridescence value from the gradient map: float4 iridescence = tex1D( gradientMap, fGradientIndex ); Iridescence is a view-dependent effect Scale and bias gradient map index to make iridescence change quicker across the wings Sample gradient map based on the computed index Resulting iridescence image:

50 August 2003 Assembling Final Color // Compute glossy highlights using values from gloss map: float fGlossValue = fGloss * ( saturate( dot( vNormal, Half )) * gloss_scale + gloss_bias ); // Assemble the final color for the wings baseColor += fGlossValue * iridescence; Assemble final wings color Compute gloss value based on the original gloss map input and dot product

51 August 2003 HLSL Disassembly Comparison ps.2.0 def c0, 0,.5, 1, 2 def c1, 4, 0, 0, 0... texld r1, t0, s1 mad r1.xyz, r1, c0.w, -c0.z dp3_sat r4.y, r1, t2 dp3_sat r4.w, r1, -t2 texld r0, t0, s0 mul r4.w, r4.w, r0.a mad r5.w, r4.w, c1.x, r4.y add r5.rgb, r5.w, c3 mul r0.rgb, r0, r5 sub_sat r0.a, c0.z, r0.a dp3 r6.xy, r1, t1 dp3_sat r6.y, r1, t3 mad r6.y, r6.y, c4.x, c4.y mul r6.z, r6.y, r1.w mad r6.x, r6.x, c4.z, c4.w texld r2, r6, s2 mul r0.rgb, r0, r0.a mad r0.rgb, r6.z, r2, r0 mov oC0, r0 ps_2_0 def c6, 2, -1, 1, 0 texld r0, t0, s1 mad r2.xyz, c6.x, r0, c6.y dp3_sat r0.x, r2, t3 mov r1.w, c5.x mad r1.w, r0.x, r1.w, c3.x dp3 r0.x, r2, t1 mul r2.w, r0.w, r1.w mov r0.w, c2.x mad r0.xy, r0.x, r0.w, c0.x texld r1, r0, s2 texld r0, t0, s0 dp3_sat r4.x, r2, t2 dp3_sat r3.x, -r2, t2 add r2.xyz, r4.x, c4 mul r1.w, r0.w, r3.x mul r1.xyz, r2.w, r1 mad r2.xyz, r1.w, c1.x, r2 mul r0.xyz, r0, r2 add r0.w, -r0.w, c6.z mad r0.xyz, r0, r0.w, r1 mov oC0, r0 Hand-Tuned Assembly CodeHLSL Compiler-Generated Disassembly Code 12 ALU 3 Texture 15 Total 15 ALU 3 Texture 18 Total

52 August 2003 Example of Translucent Iridescent Shader

53 August 2003 Optimization Study: Überlight Flexible light described in JGT article Lighting Controls for Computer Cinematography by Ronen Barzel of Pixar Überlight is procedural and has many controls: –light type, intensity, light color, cuton, cutoff, near edge, far edge, falloff, falloff distance, max intensity, parallel rays, shearx, sheary, width, height, width edge, height edge, roundness and beam distribution Code here is based upon the public domain RenderMan® implementation by Larry Gritz

54 August 2003 Überlight Spotlight Mode Spotlight mode defines a procedural volume with smooth boundaries Shape of spotlight is made up of two nested superellipses which are swept along direction of light Also has smooth cuton and cutoff planes Can tune parameters to get all sorts of looks

55 August 2003 Überlight Spotlight Volume Roundness = ½

56 August 2003 Überlight Spotlight Volume Outer swept superellipse Inner swept superellipse a b Roundness = 1 B A

57 August 2003 Original clipSuperellipse() routine float clipSuperellipse ( float3 Q, // Test point on the x-y plane float a, // Inner superellipse float b, float A, // Outer superellipse float B, float roundness) // Same roundness for both ellipses { float x = abs(Q.x), y = abs(Q.y); float re = 2/roundness; // roundness exponent float q = a * b * pow (pow(b*x, re) + pow(a*y, re), -1/re); float r = A * B * pow (pow(B*x, re) + pow(A*y, re), -1/re); return smoothstep (q, r, 1); } Computes attenuation as a function of a points position in the swept superellipse. Directly ported from original RenderMan source Compiles to 42 cycles in ps_2_0, 40 cycles on R3 x 0 Separate calculations of absolute value Computes ellipse roundness exponent for every point

58 August 2003 Vectorized Version float clipSuperellipse ( float2 Q, // Test point on the x-y plane float4 aABb, // Dimensions of superellipses float2 r) // Two precomputed functions of roundness { float2 qr, Qabs = abs(Q); float2 bx_Bx = Qabs.x * aABb.wzyx; // Swizzle to unpack bB float2 ay_Ay = Qabs.y * aABb; qr.x = pow (pow(bx_Bx.x, r.x) + pow(ay_Ay.x, r.x), r.y); qr.y = pow (pow(bx_Bx.y, r.x) + pow(ay_Ay.y, r.x), r.y); qr *= aABb * aABb.wzyx; return smoothstep (qr.x, qr.y, 1); } Precompute functions of roundness in app Vectorize abs() and all of the multiplications Compiles to 33 cycles in ps_2_0, 28 cycles on R3 x 0 Contains precomputed 2/roundness and –roundness / 2 parameters Compute b * x and B * x in a single instruction and a * y and A * y in another instruction Final result computation that feeds into smoothstep() function Vectorized computation of the absolute value

59 August 2003 smoothstep() function Standard function in procedural shading Intrinsics built into RenderMan and DirectX HLSL: 0 1 edge0edge1

60 August 2003 C implementation float smoothstep (float edge0, float edge1, float x) { if (x < edge0) return 0; if (x >= edge1) return 1; // Scale/bias into [0..1] range x = (x - edge0) / (edge1 - edge0); return x * x * (3 - 2 * x); }

61 August 2003 HLSL implementation float smoothstep (float edge0, float edge1, float x) { // Scale, bias and saturate x to 0..1 range x = saturate((x - edge0) / (edge1 – edge0)); // Evaluate polynomial return x * x * (3 – 2 * x); } The free saturate handles x outside of [edge0..edge1] range

62 August 2003 Vectorized HLSL Implementation float3 smoothstep3 (float3 edge, float3 OneOverWidth, float3 x) { // Scale, bias and saturate x to [0..1] range x = saturate( (x - edge) * OneOverWidth ); // Evaluate polynomial return x * x * (3 – 2 * x); } Operation performed on float3 s to compute three different smoothstep operations in parallel Precompute 1/(edge1 – edge0) –Done in the app for edge widths at cuton and cutoff planes With these optimizations, the entire spotlight volume computation of ü berlight compiles to 47 cycles in ps_2_0, 41 cycles on R3x0

63 August 2003 Summary Writing optimal HLSL code –Compiling issues –Optimization strategies –Code structure pointers Shader Examples –Shipped with RenderMonkey version 1.0 see www.ati.com/developerwww.ati.com/developer Iridescent Butterfly.rfx MultiTone Car Paint.rfx


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