OpenGL Rendering Pipeline and Programmable Shaders

Size: px

Start display at page:

Download "OpenGL Rendering Pipeline and Programmable Shaders"

Scot Peter White
5 years ago
Views:

1 h gpup Topics OpenGL Rendering Pipeline and Programmable s sh gpup Rendering Pipeline Types OpenGL Language Basics h gpup EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

2 h gpup 2 sh gpup 2 Pipeline: An organization or sotware and hardware which deines a ixed sequence o stages. Each stage carries out some operation, receiing its input data rom the prior stage and proiding its output data to the next stage. The order o data in the pipeline cannot change. Rendering Pipeline: An organization or the set o steps needed to conert a set o ertices into a rame buer image. The term rendering pipeline might be used generically or it might reer to something ery speciic. Clipping is the most tedious step in the rendering pipeline.. OpenGL Rendering Pipeline: The sequence o steps deined by OpenGL that start with a ertex and its attributes and usually result in the rame buer being written. Rendering Pass: The use o the rendering pipeline to render some set o primities. h gpup 2 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

3 h gpup 3 sh gpup 3 OpenGL Rendering Pipelines Deined by the OpenGL standard. Current is 4.5. h gpup 3 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

4 h gpup 4 sh gpup 4 Deinitions Stage: A pipeline section. Programmable Stage (or Unit): An OpenGL RP stage which can perorm its operation by executing user-proided sotware. Fixed-Function Stage (or Unit): An OpenGL RP stage which cannot be programmed, it s unctionality is speciied by the standard and proided by the implementation. : A program set up to run in a programmable stage, or the programmable stage itsel. h gpup 4 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 4

5 h gpup 5 sh gpup 5 Simpliied OpenGL Rendering Pipeline Programmable Unit Rendering Pipeline Input (From CPU or Buer Object) Vtx Vertex Vtx 2 3 Geometry >= Rasterizer >> Vertex Primitie () ment 0 or Frame Buer Update Fixed Function Unit Input Output ment h gpup 5 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 5

6 h gpup 6 Rendering Pass Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup 6 glbegin(gl_triangle_strip); glcolor3(lsu_spirit_gold); or ( int i=0; i<size; i++ ) ment 0 or Frame Buer Update glnormal3(norms[i].x,norms[i].y,norms[i].z); glvertex3(coords[i].x,coords[i].y,coords[i].z); } glend(); The execution o glbegin starts a rendering pass. Commands such as gldraw also start rendering passes. The rendering pass is complete ater glend inishes. During the rendering pass the CPU sends ertices into the start o the rendering pipeline which results in the rame buering being updated at the RP end. h gpup 6 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 6

7 h gpup 7 Vertex Inputs Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup 7 glbegin(gl_triangle_strip); glcolor3(lsu_spirit_gold); or ( int i=0; i<size; i++ ) ment 0 or Frame Buer Update glnormal3(norms[i].x,norms[i].y,norms[i].z); glvertex3(coords[i].x,coords[i].y,coords[i].z); } glend(); Each ertex in this example has the ollowing attributes: A coordinate (speciied by glvertex3). A normal (speciied by glnormal3). A color (speciied by glcolor3). Each execution o glvertex3 sends one ertex into the ertex shader. In the diagram a ertex, including all its attributes, shown as,, etc. h gpup 7 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 7

8 h gpup 8 The Vertex Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup 8 Input: One ertex. ment 0 or Frame Buer Update Output: One ertex. Historical Role: Compute lighted color o ertex. Conert object-space coordinates to clip space. Current Role: Proide data or geometry shader (completely user determined). I no geometry shader, output must include clip-space coordinates. h gpup 8 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 8

9 h gpup 9 The Geometry Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup 9 Input: One primitie. ment 0 or Frame Buer Update Output zero or more primities. Input primitie type must be compatible with primitie speciied by glbegin or gldraw. Input data is an array o ertex shader outputs the size o the array is determined by primitie type. Output primitie type can be reely chosen. Current Role: Must write clip-space coordinates to gl Position. Also writes whateer other data ragment shader needs. h gpup 9 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 9

10 gpup 0 Rasterizer Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup Input: One primitie (type determined by geometry shader). ment 0 or Frame Buer Update Output: Zero or more ragments one ragment or each pixel that the primitie coers. The data or each ragment is some combination o the data or each ertex in the input primitie. The rasterizer cannot be programmed. gpup 0 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

11 gpup ment Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup Input: One ragment. ment 0 or Frame Buer Update Output: Zero or one ragments. Typical Role: Read texels and blend with lighted color. gpup EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

12 gpup 2 Frame Buer Update Vtx Vertex Vtx Geometry >= 0 Rasterizer >> sh gpup Input one ragment. Output: None. ment 0 or Frame Buer Update Typical Role Applies depth, stencil, and other tests to ragment. Blends or writes passing ragment to color plane o rame buer. Frame buer update is not programmable. gpup 2 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

13 gpup 3 Data Access by s Input One set or each ertex. Vertex One set or all ertices. sh gpup Categories inputs and outputs. Uniorm ariables. Buer objects. Inputs and Outputs Vertex Normal Color MultiTexCoord0 my_s_input User-Deined Compatibility Proile-Deined Uniorm Vars glmodelviewmatrix, etc. Buer Object Position FrontColor TeXCoord[] my_s_out Data read and written by shader code. One set o data or each ertex, primitie, or ragment. To aoid waste, should not include alues common to all. For example, don t make color a shader input i all ertices are the same color, use a uniorm instead. gpup 3 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

14 gpup 4 Data Access by s Input One set or each ertex. Vertex One set or all ertices. sh gpup Uniorm Variables One set o data shared by all. Read only. Size is limited, typically 64 kib. Vertex Normal Color MultiTexCoord0 my_s_input User-Deined Compatibility Proile-Deined Usually cached (especially i < 8 kib accessed). Uniorm Vars glmodelviewmatrix, etc. Buer Object Position FrontColor TeXCoord[] my_s_out Data read and written by shader code. gpup 4 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

15 gpup 5 Data Access by s Input One set or each ertex. Vertex One set or all ertices. sh gpup Buer Objects Shared by all (ertices, primities, ragments). Can be read and written, typically as an array. Size is large. Vertex Normal Color MultiTexCoord0 my_s_input User-Deined Compatibility Proile-Deined Uniorm Vars glmodelviewmatrix, etc. Buer Object Position FrontColor TeXCoord[] my_s_out Data read and written by shader code. Usually not cached. gpup 5 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

16 gpup 6 OpenGL s sh gpup Vertex Processor ment Processor Vertex Normal Color MultiTexCoord0 Position FrontColor TeXCoord[] Color TeXCoord[] Color Depth gpup 6 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

17 gpup 7 Preparation Major Rendering Pipeline Steps sh gpup These actiities are perormed beore inoking pipeline. CPU speciies transorms, material properties, etc. Calling, say, gltranslate, helps set up pipeline but does not start it running or eed it data. Feed Data to Pipeline Data enters in a unit including a ertex and its attributes. This initiates the steps. gpup 7 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

18 gpup 8 sh gpup Vertex Processing Steps (By GPU or each ertex.) Apply modeliew transorm to ertex. Main result is ertex coordinate in eye space. Compute lighted color o ertex. Main result is lighted color. Apply projection transorm to eye-space ertex. Result is ertex coordinate in clip space. gpup 8 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

19 gpup 9 sh gpup Primitie Assembly Steps These steps operate on a primitie (a group o primities). Primitie Assembly (Group ertices into a primitie). Result is, say, a group o 3 describing a triangle. Clip (remoe) o-screen parts o primitie. Result is ewer and maybe dierent primities. Rasterize Result is the set o ragments (b locations) coered by primitie. gpup 9 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup

20 gpup 20 sh gpup 2 ment Processing Steps These steps operate on a ragment. Fetch texels, ilter and blend. Result is a rame-buer ready color. Frame Buer Update I ragment passes depth and other tests, write or blend. gpup 20 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

21 gpup 2 Programmable Units sh gpup 2 Programmable Unit: Part o the pipeline that can be programmed (as deined by some API). Choice o what is and isn t programmable constrained by: Need to allow or parallel (multithreaded, SIMD, MIMD) execution. Simple memory access. gpup 2 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

22 gpup 22 sh gpup 2 Major OpenGL Programmable Units Vertex Processor: Transorm ertex and texture coordinates, compute lighting. Geometry Processor: Using a transormed primitie and its neighbors generates new primities. For example, replace one triangle with many triangles to more closely match a cured surace. ment Processor: Using interpolated coordinates, read iltered texels and combine with colors. gpup 22 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

23 gpup 23 Languages sh gpup 2 : A programmable part o a GPU. The name shader is now misleading but is still in common use. Language: An language or programming shaders. gpup 23 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

24 gpup 24 High-Leel Languages sh gpup 2 High-Leel Languages OpenGL Language OpenGL standard. Syntax ery similar to C. Language designed or ertex and ragment shaders. Cg Originated with ATI, adopted in Direct3D. Syntax ery similar to C. Language designed or stream programs geometry, ertex, and ragment programs can be in stream orm. gpup 24 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

25 gpup 25 OpenGL Language (OGSL) sh gpup 2 OpenGL Language Important Features C-like CPP-like preprocessor directies. Library o useul geometry unctions. Includes ector and matrix types and operators. gpup 25 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

26 gpup 26 Example OGSL Data Types Example sh gpup 2 ec4 ertex_e = gl_modelviewmatrix * o_point; ec3 norm_e = gl_normalmatrix * gl_normal; ec4 light_pos = gl_lightsource[].position; loat phase_light = dot(norm_e, normalize(light_pos - ertex_e).xyz); loat phase_user = dot(norm_e, -ertex_e.xyz); loat phase = sign(phase_light) == sign(phase_user)? abs(phase_light) : 0.0; gpup 26 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

27 gpup 27 Storage Qualiiers OGSL Storage Qualiiers sh gpup 2 Used in a ariable declaration, speciies where data stored. Below, in, uniorm, constant, and out are storage qualiiers. in ec4 orce; uniorm loat x; const int sides = 5; out ec2 nudge; // Input to this shader, dierent or each primitie. // Input to shader, alue rarely changed. // Can neer be changed. // Output o this shader (input to some other). gpup 27 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

28 gpup 28 sh gpup 2 Storage Qualiier Types uniorm: Read-only by shader. Written by client, change is time consuming. Typical use: transormation matrices. in: Input to shader. Read-only by shader that made the in declaration. Value is set either by client (using glvertexattrib and riends) or by a prior stage shader (by writing an out ariable. Typical uses: ertex material properties (color), normal. out: Output o shader. Value is written by shader in which out declaration appears and read by shader in subsequent stage. sampler: Read-only by ertex and ragment shader. A handle to a texture unit, used by texture access unctions. gpup 28 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

29 gpup 29 sh gpup 2 Interpolation Qualiiers Used or ragment shader inputs. Speciy how alue should be interpolated. lat: No interpolation. smooth: Perspectie-correct interpolation. noperspectie: Linear interpolation. gpup 29 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 2

30 gpup 30 sh gpup 3 Deprecated Storage Qualiiers. These were used in earlier ersions o OGSL. They hae been replaced by in and out. attribute: Deprecated. Like an in but only can be used or ertex shader. arying: Deprecated. When used in a ertex shader is the same as out, when used in a ragment shader is the same as in. gpup 30 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

31 gpup 3 sh gpup 3 Storage Qualiier Example // For ertex and ragment shaders: uniorm ec3 graity_orce; uniorm loat gs_constant; uniorm ec2 ball_size; // Vertex Only in loat step_last_time; in ec4 position_let, position_right, position_aboe, position_below; in ec3 ball_speed; out ec4 out_position; out ec3 out_elocity; // ment Only // in ec4 out_position; in ec3 out_elocity; gpup 3 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

32 gpup 32 Function Parameters OGSL Functions sh gpup 3 OpenGL Shading Language.30 Section 4.4 Call by alue. Parameter Qualiiers: in (deault) out inout Built In Functions See OpenGL Shading Language.30 Section 8 gpup 32 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

33 gpup 33 OpenGL Shading Language Use sh gpup 3 Steps or adding a typical shader to existing OpenGL code: Deine what the shader is supposed to do. Identiy appropriate programmable units (ertex, geometry, ragment, etc). Identiy data that shaders will use. I data rom client (CPU) determine whether attribute or uniorm. For attributes and uniorms, determine i pre-deined or user-deined. Write shader code. In CPU code ollow steps or installing shader. (E.g., use p). Get names o any new uniorms and attributes. As necessary, initialize uniorms and attributes. Turn shader on and o as necessary. gpup 33 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

34 gpup 34 Example Phong sh gpup 3 Phong : A lighting model in which the lighted color is computed at each ragment. (Otherwise the lighted color is computed at each ertex o a primitie and those lighted colors are interpolated across the ragments.) Phong Steps Deine what shader does. Computes lighting at ragment using interpolated normal... Identiy appropriate units. For computing lighting: ragment shader. For passing along normal and color ino, ertex shader. Identiy data that shaders use. VS: Lighting data, normal. (All pre-deined.) FS: Normal (interpolated), eye-space ertex coordinates. User de. gpup 34 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

35 gpup 35 sh gpup 3 OpenGL Calls, rom Initialization to Use (See OGL 4.3 Chapter 7) Create Program Object (Once) pobject = glcreateprogram() For Each (Vertex, Geometry, ment, etc.): Create Object sobject = glcreate(gl VERTEX SHADER) Proide Source Code to Object and Compile glsource(sobject,,&shader text lines,null); glcompile(sobject); Attach glattach(pobject,sobject); Link (Once) gllinkprogram(pobject); Use (Many Times, e.g., once per rame.) gluseprogram(pobject); gpup 35 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

36 gpup 36 OGSL Use sh gpup 3 Obtaining and Using Variable Reerences At run time ariables identiied by number. At Initialization get location (index) o attributes and uniorms: sal pinnacle = glgetattriblocation(pobject,name); sun ball size = glgetuniormlocation(pobject,name); During Render (Inrequently) Change Uniorm Value (Using location) gluniorm2(sun ball size,ball size,ball size sq); During Render (Per Vertex Okay) Change Attribute Value (Using location) glvertexattrib4(sal pinnacle,pinnacle.x,pinnacle.y,pinnacle.z,radius); Done beore each glvertex. Same options as ertex, such as client and buer object arrays. gpup 36 EE Lecture Transparency. Formatted 8:06, 7 December 205 rom rendering-pipeline. sh gpup 3

OpenGL Rendering Pipeline and Programmable Shaders

h gpup Topics OpenGL Rendering Pipeline and Programmable s sh gpup Rendering Pipeline Types OpenGL Language Basics h gpup EE 4702- Lecture Transparency. Formatted 8:59, 29 September 206 rom rendering-pipeline.