OpenGL Shading Language Hints/Kinks

Transcription

1 OpenGL Shading Language Hints/Kinks Bill Licea-Kane AMD Copyright Khronos Group, Page 1

2 OpenGL Shading Language Hints/Kinks Made in the Shade A brief WABAC Machine moment Our world is no longer side effect free - (GL_ARB_conservative_depth) - GL_ARB_shader_image_load_store - GL_ARB_shader_atomic_counters Some examples - Don't try this at home - Something old school - Something new school Copyright Khronos Group, Page 2

3 Brief WABAC Machine moment A decade in the shade OpenGL Birds of a Feather Wednesday, 15 August, 6:30 pm - 8:30 pm Wilshire Grand, Wilshire Room Copyright Khronos Group, Page 3

4 Shader-centric view The way things were side effect free Uniforms Textures in Shader out Temporaries Copyright Khronos Group, Page 4

5 Shader-centric view The way things are side effects! Uniforms Textures Images in Shader out Temporaries Copyright Khronos Group, Page 5

6 Shader-centric view but still embarrassingly parallel Copyright Khronos Group, Page 6

7 memory qualifiers memory functions // memory qualifiers coherent volatile restrict writeonly readonly // memory functions void memorybarrier(); Copyright Khronos Group, Page 7

8 built-in functions gvec4 imageload(readonly IMAGE_PARAMS) void imagestore(writeonly IMAGE_PARAMS, gvec4 data) Copyright Khronos Group, Page 8

9 built-in functions continued int imageatomicadd(image_params, int data) int imageatomicmin(image_params, int data) int imageatomicmax(image_params, int data) int imageatomicand(image_params, int data) int imageatomicor(image_params, int data) int imageatomicxor(image_params, int data) int imageatomicexchange(image_params, int data) int imageatomiccompswap(image_params, int compare, int data) Copyright Khronos Group, Page 9

10 built-in functions continued uint imageatomicadd(image_params, uint data) uint imageatomicmin(image_params, uint data) uint imageatomicmax(image_params, uint data) uint imageatomicand(image_params, uint data) uint imageatomicor(image_params, uint data) uint imageatomicxor(image_params, uint data) uint imageatomicexchange(image_params, uint data) uint imageatomiccompswap(image_params, uint compare, uint data) Copyright Khronos Group, Page 10

11 built-in functions continued uint atomiccounterincrement (atomic_uint c) uint atomiccounterdecrement (atomic_uint c) uint atomiccounter (atomic_uint c) Copyright Khronos Group, Page 11

12 We would rather not shade if possible Some controls to help layout (depth_any) out float gl_fragdepth; // [unhappy face] // hints // may allow depth test early, gl_fragdepth will be written layout (depth_unchanged) out float gl_fragdepth; // [happy face] layout (depth_greater) out float gl_fragdepth; // [half-happy face] layout (depth_less) out float gl_fragdepth; // [half-happy face] // early depth test, period. gl_fragdepth ignored layout (early_fragment_tests) in; // [woot-woot face] Copyright Khronos Group, Page 12

13 Examples - Don t try this at home We are what you call "experts" // "Experts" wouldn t do this either. // For thought-experimentation ONLY!!! // Seriously. layout (early_fragment_tests) in; layout (binding=0, offset=0) uniform atomic_uint counter; void main() { atomiccounterincrement(counter); } Copyright Khronos Group, Page 13

14 Examples - Don t try this at home Occlusion querry-ish // "Experts" wouldn t do this either. // For thought-experimentation ONLY!!! // Seriously. layout (early_fragment_tests) in; layout (binding=0, offset=0) uniform atomic_uint counter; void main() { atomiccounterincrement(counter); } Copyright Khronos Group, Page 14

15 Examples Something old school layout (triangles) in; layout (points, max_vertices=1) out; //... bool classifytriangle(); void emithit(); void main() { if classifytriangle() emithit(); } Copyright Khronos Group, Page 15

16 Examples Something old school Selection Mode layout (triangles) in; layout (points, max_vertices=1) out; //... bool classifytriangle(); void emithit(); void main() { if classifytriangle() emithit(); } Copyright Khronos Group, Page 16

17 Examples something new school Per fragment (even per sample) selection Based on example from GDC OIT and Indirect Illumination using DX11 Linked Lists Holger Gruen, Nicolas Thibieroz, AMD ISV Relations Create a selection-sized offset image (4x4) Bind headoffset and datastore images Bind counter buffer Initialize headoffset and counter Setup scissor DISABLE depth testing (we want EVERYTHING in the list) No framebuffer output Render Copyright Khronos Group, Page 17

18 Examples something new school Images headoffset and datastore offset link id depth Copyright Khronos Group, Page 18

19 Examples something new school Images 1 st triangle offset link id depth -1 id-red depth-red Copyright Khronos Group, Page 19

20 Examples something new school Images 2 nd triangle offset link id depth -1 id-red depth-red -1 id-green depth-green Copyright Khronos Group, Page 20

21 Examples something new school Images 3 rd triangle offset link id depth -1 id-red depth-red -1 id-green depth-green -1 id-cyan depth-cyan -1 id-cyan depth-cyan -1 id-cyan depth-cyan Copyright Khronos Group, Page 21

22 Examples something new school Images n th triangle offset f link id depth -1 id-red depth-red -1 id-green depth-green -1 id-cyan depth-cyan -1 id-cyan depth-cyan -1 id-cyan depth-cyan 0 id-blue depth-blue Copyright Khronos Group, Page 22

23 Examples Something new school layout (binding=0, offset=0) uniform atomic_uint fragmentcounter; layout (r32ui) coherent uniform image2d restrict headoffset; layout (rgba32ui) writeonly uimagebuffer restrict datastore; int2 coord(); // transform to coordinate system of headoffset buffer uvec3 data(); // id, depth, whatever (color?) void main() { uint NewOffset, PrevOffset; NewOffset = atomiccounterincrement(fragmentcounter); PrevOffset = imageatomicexchange(headoffset, coord(), NewOffset); imagestore(datastore, NewOffset, uvec4(prevoffset, data())); } Copyright Khronos Group, Page 23

24 OpenGL Shading Language Hints/Kinks Thank you! Copyright Khronos Group, Page 24