Shader Programming

8/16/2019 Shader Programming

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Shader programmingBased on Jian Huang’s lecture on Shader Programming


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What OpenGL could do 20 years ago


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What OpenGL could do ' years ago


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What’s (hanged)

* 20 years ago:* +rans,orm -ertices !ith model-ie!pro&ection matrices"

* Shade !ith Phong lighting model only"

* .o!:* (ustom -erte/ trans,ormation"

* (ustom lighting model"

* ore complicated -isual e,,ects"

* Shado!s* 1isplaced and detailed sur,aces

* Simple re,lections and re,ractions

* tc"


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What’s (hanged)

* 20 years ago:* 3erte/ trans,ormation,ragment shading hardcoded into GP4s"

*

.o!:* ore parts o, the GP4 are programma%le 5%ut not all6"


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Shader Program

* 7 small program to control parts o, the graphics pipeline

* (onsists o, 2 5or more6 separate parts:* 3erte/ shader controls -erte/ trans,ormation"

* 8ragment shader controls ,ragment shading"


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3erte/ Shader

* +rans,orm -ertices ,rom o%&ect space to clip space"* (on-entionally model-ie! ,ollo!ed %y pro&ection

* (an de,ine custom trans,ormation to clip space

* (ompute other data that are interpolated !ith -ertices"* (olor

* .ormals

* +e/ture coordinates

* tc"


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What (an a 3erte/ Shader 1o)

1isplaceddistorted sur,aces


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What (an a 3erte/ Shader 1o)

Skinning/Animation


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8ragment Shader

* (ompute the color o, a ,ragment 5i"e" a pi/el6"

* +a#e interpolated data ,rom -erte/ shaders"

* (an read more data ,rom:* +e/tures

* 4ser speci,ied -alues"


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What (an a 8ragment Shader 1o)

ore (omplicated9 1etailed aterials* Glossy

* e,lecti-e9 re,racti-e

* ough9 %umpy9 lots o, noo#s and crannies

* Wooden


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What (an a 8ragment Shader 1o)

Shado!s 5including so,t edges;6

http:!!!",a%iensanglard"netshado!mappingP(8


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GLSL


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GLSL

* Similar to ((>>

* 4sed to !rite shaders

* 3erte/9 tessellation9 geometry9 ,ragment

* We only co-er -erte/ and ,ragment here

* Based on OpenGL

* 8irst a-aila%le in OpenGL 2"0 5200?6

* (ompetitors:

* .-idia (g

* icroso,t HLSL


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GLSL Program

* Speci,ies ho! OpenGL should dra! geometry"

* Program: 7 collection o, shaders that run together"* 7t least one -erte/ shader or one ,ragment shader"

* Should ha-e %oth so !e #no! its %eha-ior completely"

* 7t any time9 the GP4 runs only one program"* ust speci,y program to use %e,ore dra!ing geometry"


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Shader

* Shader source code resem%les ((>> source code"* Similar data types9 e/pressions9 and control statements"

* 8unctions are !ritten in the same !ay"

* ntry point @ A-oid main5 6* .ot Aint main5int argc9 char CCarg-6 as in normal ("

* +!o main ,unctions !hen !riting a -erte/ shader and a

,ragment shader together"


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Shader Structure

/*Multiple-lined comment

*/

// Single-lined comment

//// Global variable definitions

//

void main()

{

//

// Function body

//

}


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Green shader


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3erte/ Shader

Green.vert:

version !"#

uniform mat$ un%&ro'ection

uniform mat$ un%Modelie

attribute vec+ in%erte,

void main()

{

gl%&osition un%&ro'ection * un%Modelie * vec$(in%erte,. !)}


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Green.vert:

version !"#




void main()

{


3erte/ Shader

ach time the screen is dra!n9 thismain56 ,unction is called once per -erte/9 as i, it !ere in a ,or loop"


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3erte/ Shader

+he ,irst thing to do is speci,y theGLSL -ersion" We use -ersion D"20in this class" 5.ote: other -ersionscan %e -ery di,,erent;6

Green.vert:

version !"#




void main()

{



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3erte/ Shader

4ni,orms are one type o, input to theshader" +hey are the same ,or each-erte/ dra!n during one dra!,unction" We !ill see ho! to set them

later" +hese ones are thecon-entional pro&ection andmodel3ie! matrices"

Green.vert:

version !"#




void main()

{



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3erte/ Shader

7ttri%ute -aria%les lin# to -erte/attri%utes9 or data associated !itheach -erte/" +his one is set to the-erte/ position %u,,er" ach timemain56 is e/ecuted9 in=3erte/ is setto the -erte/ currently %eingprocessed"

Green.vert:

version !"#




void main()

{



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3erte/ Shader gl=Position is a special -aria%le thatholds the position o, the -erte/ in clip

space"

Since a -erte/ shader’s main outputis the position in clip space9 it mustalways set gl=Position"

+his -erte/ shader &ust trans,ormseach -erte/ position %y thepro&ection9 model9 and -ie! matrices"

Green.vert:

version !"#




void main()

{



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8ragment Shader

Green.frag:

version !"#



void main()

{

gl%Fragolor vec$(#.!.#.!)

}


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8ragment Shader

ach time the screen isdra!n9 this main56 ,unctionis called once per pi/el"

Green.frag:

version !"#



void main()

{


}


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8ragment Shader

gl=8rag(olor is a special-aria%le that stores thecolor o, the output,ragment"

Since a ,ragment shader computes the color o, a,ragment9 it must always set gl=8rag(olor"

Green.frag:

version !"#



void main()

{


}


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8ragment Shader

-ec? is a data type o, ?1-ector"

(an %e used to store: $homogeneous coordinates $GB7 color

-ec?509D909D6 constructs an

GB7 tuple !ith @09 G@D9B@09 7@D9 !hich is green"

Green.frag:

version !"#



void main()

{


}


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OpenGLGLSL Plum%ing

* Suppose !e ha-e already created the program

* We tell OpenGL to use it"

* We then instruct OpenGL to dra! a triangle:

Green.java:// 01e vertices in our verte, buffer. initiali2ed earlierfloat 34 vertices {-#56. -#56. #. -#56. -#56. #. #. #56. # }//555

// 7n t1e dra met1odprogram5use()

gl8ra9lements(555)

G:&rogram5unuse()


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Green+riangle1emo


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4sing GLSL in Ja-a


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+o use a GLSL programE

* 8ollo! the ,ollo!ing F steps"

D" (reate shader o%&ects"

2" ead source code ,rom ,iles and ,eed them to the shader o%&ects &ust created"

" (ompile the shader"

?" (reate a program o%&ect"

'" 7ttach the shaders to the program"" Lin# the program"

F" +ell OpenGL to use your shader program"


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+o use a GLSL programE

* 8ollo! the ,ollo!ing F steps"

D" (reate shader o%&ects"

2" ead source code ,rom ,iles and ,eed them to the shader o%&ects &ust created"

" (ompile the shader"

?" (reate a program o%&ect"

'" 7ttach the shaders to the program"" Lin# the program"

F" +ell OpenGL to use your shader program"

W H 7+ 7 P 7I . ;


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(S ?20 8rame!or#

* (ontains GLProgram class to a%stract OpenGL calls;– 7dded con-enience methods

– Help #eep con-entions straight

– (ontrols mapping %et!een attri%ute -aria%les and-erte/ %u,,ers


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.o!9 to create a GLSL programE

* (reate a GLProgram o%&ect"

rivate GLProgram program;

ublic void onEntry(GameTime gameTime) {

program = new GLProgram();program.quic!reate"e#ource(

$c#%&'glGrid.vert$* Pat+ to verte, #+ader $c#%&'glGrid.-rag$* Pat+ to -ragment #+ader

null); ptional attribute li#t /


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.o!9 to use a GLSL programE

* 4se it" 1ra! stu,," 4nuse it 5i, need %e6"

ublic void draw(GameTime gameTime) { 0#e our GL1L program

program.u#e();

Tell penGL to draw our me#+ gl2rawElement# (GL3T"456GLE1 * inde,!ount* GLType.0n#igned4nt * );

!lean up GLProgram5unu#e ();

/


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GLSL 17+7 +PS


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GLSL 1ata +ypes

* Both GLSL and Ja-a* ,loat9 int

* GLSL has9 %ut Ja-a has not* -ec29 -ec9 -ec?: -ectors

* mat29 mat9 mat?: matrices

* samplerD19 sampler219 sample19 sampler(u%e9 etc: te/tures

* Ja-a has9 %ut GLSL has not* O%&ect

* String

* etc


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-ec2

* epresents a -ector in 21" ach component is a ,loat"

vec" a;

a., = #5#;

a.y = !5#; // a (#.!)

vec" b;

b.s = !#5#;

b.t = !"56; // b (!#.!"56)

vec" c;

c[#] = ;5#;

c[!] =


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-ec2

float p = a.t; // p !

float = = b[!] + c., // = "!56

vec" d = vec"(+, c.y * "); // d (+.!>)

vec" d = a + b; // d (!#.!+56)

vec" e = b - c; // e (!.$56)

vec" f = b * c; // f (;#.!##)

vec" g = + * a; // g (#.+)

float 1 = lengt1(c); // 1 !"5#$"


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-ec

vec+ a;

a., = !#5#; a.y = "#5#; a.2 = +#5#; // a (!#. "#. +#)

a.r = #5!; a.g = #5"; a.b = #5+; // a (#5!. #5". #5+)

a.s = !5#, a.t = "5#; a.p = +5#; // a (!. ". +)

vec+ b = vec+($5#, 65#, >5#);

vec+ c = a + b; // c (6. ?. ;)

vec+ d = a - b; // d (-+. -+. -+)

vec+ e = a * b; // e ($. !#. !. ;)

float g = dot(a,b); // g +"

vec+ 1 = cross(a,b); // 1 (-6.>.-+)

float i = lengt1(a); // i +5?$"


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-ec?

vec$ a;

a., = !#5#; a.y = "#5#; a.2 = +#5#; a. = $#5#;

// a (!#. "#. +#. $#)

a.r = #5!; a.g = #5"; a.b = #5+; a.a = #5$;

// a (#5!. #5". #5+. #5$)

a.s = !5#; a.t = "5#; a.p = +5#; a.= = $5#;

// a (!. ". +. $)

vec$ b = vec$(6, >, ?, . . ;. !")

float g = lengt1(a); // g 65$??


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mat2

* epresents a 2 %y 2 matri/" ach component is a ,loat"

mat" @ = mat"(!5#, "5#, +5#, $5#); // in column-ma'or order

vec" , = vec"(!5#, #5#);

vec" y = vec"(#5#, !5#);

vec" a = @ * ,; // a (!.")

vec" b = @ * y; // b (+.$)


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mat

mat+ @ = mat+(!5#, "5#, +5#, $5#, 65#, >5#, ?5#,


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7rray

* We can declare ,i/ed$siKe arrays 5siKe #no!n at compile

time6

* 4se ( synta/"

float @[$];

@[#] = 6; @[+] = !#;

vec$ A[!#];

A[+] = vec$

(!,",+,$);

A[


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S!iKKling

* 4sed to construct a -ector ,rom another -ector %y

re,erring to multiple components at one time"

vec$ a = vec$(!,",+,$);

vec+ b = a.,y2; // b (!.".+)

vec" c = a.=p; // c ($.+)

vec$ d = a.,,yy; // d (!.!.".")


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+ype (on-ersion

* Synta/: -aria%leMM @ typeMM5 -alueMM 6N

* /pression on HS @ Aconstructor e/pression"

* /ample:

float a = !5#;

int b = int(a);


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+ype (on-ersion

* We can create larger -ectors ,rom smaller ones"

vec" a = vec"(!,");

vec" b = vec"(+,$);

vec$ c = vec$(a,b); // c (!.".+.$)

vec+ d = vec+(#,#,!);

vec$ e = vec$(d,#); // d (#.#.!.#)

vec$ f = vec$(#,a,+); // f (#.!.".+)

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Shader Programming