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C++OpenGLmeshrendering
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6years,4monthsago
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6years,4monthsago
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Iknowtherearealotofresourcesaboutthisontheinternetbuttheydidn'tquiteseemtohelpme.
WhatIwanttoachieve:
Iambakingameshfromdatawhichstorestheverticesinsideavector.
(Vector3isasctructcontaingfloatx,y,z)
Itstorestrianglesinamap>
(thekeyofthemapisthesubmeshandthevectorthetriangles)
theuvinsideavector
(Vector2isastructcontainingfloatx,y)
andacolorvalueinvector
(thecolorvalueappliestoverticesliketheuvdoes)
NowIwanttowriteacodethatcanreadthatdataanddrawittothescreenwithmaximumperformance
WhatIgot:
staticvoidrenderMesh(Meshmesh,floatx,floaty,floatz){
if(mesh.triangles.empty())return;
if(mesh.vertices.empty())return;
if(mesh.uvs.empty())return;
glColor3f(1,1,1);
typedefstd::map>::iteratorit_type;
for(it_typeiterator=mesh.triangles.begin();iterator!=mesh.triangles.end();iterator++){
intsubmesh=iterator->first;
if(submeshsecond.size();i+=3){
intt0=iterator->second[i+0];
intt1=iterator->second[i+1];
intt2=iterator->second[i+2];
Vector3v0=mesh.vertices[t0];
Vector3v1=mesh.vertices[t1];
Vector3v2=mesh.vertices[t2];
Colorc0=mesh.vertexColors[t0];
Colorc1=mesh.vertexColors[t1];
Colorc2=mesh.vertexColors[t2];
Vector2u0=mesh.uvs[t0];
Vector2u1=mesh.uvs[t1];
Vector2u2=mesh.uvs[t2];
glBegin(GL_TRIANGLES);
glColor4f(c0.r/255.0f,c0.g/255.0f,c0.b/255.0f,c0.a/255.0f);glTexCoord2d(u0.x,u0.y);glVertex3f(v0.x+x,v0.y+y,v0.z+z);
glColor4f(c1.r/255.0f,c1.g/255.0f,c1.b/255.0f,c1.a/255.0f);glTexCoord2d(u1.x,u1.y);glVertex3f(v1.x+x,v1.y+y,v1.z+z);
glColor4f(c2.r/255.0f,c2.g/255.0f,c2.b/255.0f,c2.a/255.0f);glTexCoord2d(u2.x,u2.y);glVertex3f(v2.x+x,v2.y+y,v2.z+z);
glEnd();
glColor3f(1,1,1);
}
}
}
Theproblem:
IfoundoutthatthewayIrenderisnotthebestwayandthatyoucanachievehigherperformancewithglDrawArrays(Ithinkitwascalled).
CouldyouhelpmerewritingmycodetofitwithglDrawArrays,sincewhatIfoundsofarontheinternetdidnothelpmetoomuch.
Thanks,andifthereisanymoreinformationneededjustask.
c++openglmesh
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editedJan23,2016at15:26
Sheldon
askedJan23,2016at12:16
SheldonSheldon
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Justasuggestion:theversionofOpenGLyourarelearninghasbeendeprecatedforanumberofyears.Isuggestyouputyourtimeinlearningamoreuptodateversion.Seealso:stackoverflow.com/questions/14300569/opengl-glbegin-glend
– RichardCritten
Jan23,2016at12:30
IfyoumovefromOpenGLv1.0tov3.5-4.5youwilltransitiontoGLCallsthatworkwithShadersontheGPUasopposedtoworkingontheCPU.OnceyouhavetheframeworkinplacetouseGLSLthenitcanbeveryefficienttocreateaBatchProcess.UsingBatcheswillmaximizetheamountofverticesperrendercallloweringtheamountofCPUtoGPUcallswhichwillalsoreducethebottleneckthatiscausedwhileworkingacrosstheBus.Workingwithmultiplethreadswillhelpwhereaworkerthreadcanpre-calculateandcreatestoredmemorybufferswhiletheotherthreaddoestherendercalls.
– FrancisCugler
Jan23,2016at13:37
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TheuseoffunctionslikeglBeginandglEndisdeprecated.FunctionslikeglDrawArrayshaveabetterperformance,butslightlymorecomplicatedtouse.
TheproblemofglBeginrendertechniquesisyouhavetocommunicateeachvertexonebyoneeachtimeyouwanttodrawsomething.Today,graphiccardsareabletorenderthousandsofverticesveryquickly,butifyougiveitonebyone,therenderwillbecomelaggyregardlessyourgraphiccardperformance.
ThemainadvantageofglDrawArraysisyouhavetoinitializeyourarraysonce,andthendrawitwithonecall.Sofirst,youneedtofillatthestartofyourprogramanarrayforeachattribute.Inyourcase:positions,colorsandtexturecoords.Itmustbefloatarrays,somethinglikethis:
std::vectorvertices;
std::vectorcolors;
std::vectortextureCoords;
for(inti=0;isecond.size();i+=3){
intt0=iterator->second[i+0];
intt1=iterator->second[i+1];
intt2=iterator->second[i+2];
vertices.push_back(mesh.vertices[t0].x);
vertices.push_back(mesh.vertices[t0].y);
vertices.push_back(mesh.vertices[t0].z);
vertices.push_back(mesh.vertices[t1].x);
vertices.push_back(mesh.vertices[t1].y);
vertices.push_back(mesh.vertices[t1].z);
vertices.push_back(mesh.vertices[t2].x);
vertices.push_back(mesh.vertices[t2].y);
vertices.push_back(mesh.vertices[t2].z);
//[...]Sameforcolorsandtexturecoords.
}
Then,inanotherfunctionsetonlyfordisplay,youcanusethesearraysinordertodrawit:
//Enableeverythingyouneed
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
//Setyourusedarrays
glVertexPointer(3,GL_FLOAT,0,vertices.data());
glColorPointer(4,GL_FLOAT,0,colors.data());
glTexCoordPointer(2,GL_FLOAT,0,textureCoords.data());
//Drawyourmesh
glDrawArrays(GL_TRIANGLES,0,size);//'size'isthenumberofyourvertices.
//Resetinitialstate
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
Ofcourse,you'llhavetoenableotherattributesyouwanttouse,liketextureorblending.
NOTE:
Ifyouwishtolearnaboutperformance,therearealsootherfunctionsusingindicesinordertoreducethesizeofdataused,likeglDrawElements.
TherearealsoothermoreadvancedOpenGLtechniquesthatallowsyoutoincreaseperformancebysavingyourdatadirectlyonthegraphiccardmemory,likeVertexBufferObjects.
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editedJun20,2020at9:12
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answeredJan23,2016at12:41
AracthorAracthor
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Thanks,goingtotestit."Itmustbefloatarrays"-soIcan'tuseavectorforthecolors?
– Sheldon
Jan23,2016at12:47
@SheldonTechnicallyyoucan,butyou'llhavetochangesomeparametersinmysample,likesecondargumentofglColorPointer.MostofprogramsusefloatevenforcolorsbecauseitisthefavoritetypeofOpenGLinitself.
– Aracthor
Jan23,2016at12:50
@Sheldonbecarefulofwhatyoucalla"vertex".Thethirdargumentisthenumberof"points"ofyourmesh,buteachpointhave3spacecoordinates(x,y,z).Soifyougivethesizeofthe"vertices"vectorasparameter,yougivethreetimestoomanyverticesthatyoushould,andglDrawArraysshalllooktoofaronyourarrays.
– Aracthor
Jan23,2016at13:28
Trytodisplayjustpositionswithouttextureorcolorsforstart,itshouldbeawhitemesh.Andtrytorenderitwithanon-blackandnon-whiteclearcolor,maybeitisthesamecoloratthebackgroundoneandyoudon'tseeit.
– Aracthor
Jan23,2016at13:35
ThatwasthefirstthingItried.Itdidn'trender.
– Sheldon
Jan23,2016at13:39
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