gl_FragCoord is a built-in input variables, it isn't necessary to declared the input variable gl_FragCoord . The x and y coordinate are ...
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Howtogetcoordinateoffragmentshaders?gl_FragCoordnotworking
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3years,2monthsago
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I'mtryingtomakeaMandelbrotsetexplorer,whichwillshadethepixelsonthescreenbasedonitscoordinateinthewindow.I'vedonethisbeforewithoutusingshadersbutitsextremelyslow.Ican'tfigureouthowtogetthepositionofthefragmentsothatIcanusethealgorithmI'vealreadydevelopedtorendertheMandelbrotset.
I'musingljgwl3.I'vebeenresearchingalldayonhowtodothis,andIcan'tfindanycomprehensivefindingsonhowtogetthecoordinates.Itseemslikegl_FragCoordshouldworkandthenIcouldusegl_FragCoord.xandgl_FragCoord.ytogetthexandyvalues,whichisallIneedforthealgorithm,butmyscreenalwaysendsupbeingallred.I'mnotpassinganyinfofromthevertexshaderintomyfragmentshaderbecauseIneedtorenderthecolorofeachcoordinateintheMandelbrotbasedonitsxandyvalues,sothevertexpositionsaren'thelpful(Ialsodon'tunderstandhowtogetthose).
Hereismyfragmentshader:
invec4gl_FragCoord;
uniformvec2viewportDimensions;
uniformfloatminX;
uniformfloatmaxX;
uniformfloatminY;
uniformfloatmaxY;
vec3hsv2rgb(vec3c){
vec4K=vec4(1.0,2.0/3.0,1.0/3.0,3.0);
vec3p=abs(fract(c.xxx+K.xyz)*6.0-K.www);
returnc.z*mix(K.xxx,clamp(p-K.xxx,0.0,1.0),c.y);
}
voidmain(){
floatx=gl_FragCoord.x;
floaty=gl_FragCoord.y;
vec2c=vec2((x*(maxX-minX)/viewportDimensions.x+minX),(y*(maxY-minY)/viewportDimensions.y+minY));
vec2z=c;
floatlimit=1000;
floatiterations=0;
for(inti=0;i4){
break;
}
iterations+=1.0;
}
floatitRGB=iterations/limit;
vec3hsv=vec3(itRGB,1.0,1.0);
vec3rgb=hsv2rgb(hsv);
gl_FragColor=vec4(rgb,1);
}
IthoughtthatIcouldusegl_FragCoordwithoutdeclaringitasinfirstbutitdoesn'tworkeitherway.vec2cisattemptingtomapthecurrentcoordinatetoacoordinateinthecomplexnumbergridbasedoncurrentresolutionofthewindow.
Thisisallthat'sinmyvertexshader:
voidmain(){
gl_Position=ftransform();
}
Andtherelevantbitofmyclientcode:
glBegin(GL_POLYGON);
glVertex2f(-1f,-1f);
glVertex2f(1f,-1f);
glVertex2f(1f,1f);
glVertex2f(-1f,1f);
glEnd();
Thisisrunninginmywindowloop,andjustcreatesthesquarewherethemandelbrotissupposedtorender.
ThisistheoutputofmyworkingjavaMandelbrotprogramwhichdoesn'tuseshaders:
Thisistheoutputofmyshaderprogram:
Fullscreen:
Ialsohavenoclueastohowtobeabletoresizethewindowproperlywithouttheblackbars.Iamattemptingtodothiswithvec2cinmycodeaboveasIhavesettheuniformstobethewindowsheightandwidthandamusingthatwhenmappingthecoordinatetothecomplexnumberplane,butasgl_FragCoorddoesn'tseemtoworkthenneithershouldthis.AlinktoacurrentguideonlgjwlscreenresizingbasedonglfwCreateWindowwouldbevastlyappreciated.
javaopenglglslshaderlwjgl
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editedMar24,2019at9:43
Rabbid76
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askedMar24,2019at1:26
uhinuhin
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Whatexactlydoyouexpectctobe?Areyouexpectingittobeavalueontherange[-1,1]?Whataremin/maxX/Y,andhowdotheyrelatetoviewportDimensions?
– NicolBolas
Mar24,2019at1:35
@NicolBolasCisintendedtobeacoordinateinthecomplexnumbergridthatthemandelbrotliesin.RightnowIhavethisbeingfrom[-2,2]yaxisand[-2,2]xaxis.minX,maxX,minY,maxY,definethedomainandrangeofthecomplexnumberplaneIwanttoview,andtheviewportDimensionsisintendedtobeusedtomapthosenumberstopixelvaluesofthewindow.
– uhin
Mar24,2019at14:48
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1Answer
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gl_FragCoordisabuilt-ininputvariables,itisn'tnecessarytodeclaredtheinputvariablegl_FragCoord.Thexandycoordinatearewindow(pixel)coordinate.
Thelowerleftofgl_FragCoordis(0.5,0.5)andtheupperrightis(W-0.5,H-0.5),whereWandHarethewidthandtheheightoftheviewport.
You'vetomapgl_FragCoord.xtotherange[minX,maxX]andgl_FragCoord.ytotherange[minY,maxy].
IrecommendtoustheGLSLfunctionmixforthis.
viewportDimensionsisassumedtocontainthewithandtheheightoftheviewportrectangleinwindow(pixel)coordinates.
vec2c=mix(vec2(minX,minY),vec2(maxX,maxY),gl_FragCoord.xy/viewportDimensions.xy);
Seethe(WebGL)example,whereIappliedthesuggestionstothethefragmentshaderofthequestion.
Theboundsareinitializedasfollows
minX=-2.5
minY=-2.0
maxX=1.5
maxY=2.0
(functionloadscene(){
varcanvas,gl,vp_size,prog,bufObj={};
functioninitScene(){
canvas=document.getElementById("ogl-canvas");
gl=canvas.getContext("experimental-webgl");
if(!gl)
return;
progDraw=gl.createProgram();
for(leti=0;i<2;++i){
letsource=document.getElementById(i==0?"draw-shader-vs":"draw-shader-fs").text;
letshaderObj=gl.createShader(i==0?gl.VERTEX_SHADER:gl.FRAGMENT_SHADER);
gl.shaderSource(shaderObj,source);
gl.compileShader(shaderObj);
letstatus=gl.getShaderParameter(shaderObj,gl.COMPILE_STATUS);
if(!status)alert(gl.getShaderInfoLog(shaderObj));
gl.attachShader(progDraw,shaderObj);
gl.linkProgram(progDraw);
}
status=gl.getProgramParameter(progDraw,gl.LINK_STATUS);
if(!status)alert(gl.getProgramInfoLog(progDraw));
progDraw.inPos=gl.getAttribLocation(progDraw,"inPos");
progDraw.minX=gl.getUniformLocation(progDraw,"minX");
progDraw.maxX=gl.getUniformLocation(progDraw,"maxX");
progDraw.minY=gl.getUniformLocation(progDraw,"minY");
progDraw.maxY=gl.getUniformLocation(progDraw,"maxY");
progDraw.viewportDimensions=gl.getUniformLocation(progDraw,"viewportDimensions");
gl.useProgram(progDraw);
varpos=[-1,-1,1,-1,1,1,-1,1];
varinx=[0,1,2,0,2,3];
bufObj.pos=gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER,bufObj.pos);
gl.bufferData(gl.ARRAY_BUFFER,newFloat32Array(pos),gl.STATIC_DRAW);
bufObj.inx=gl.createBuffer();
bufObj.inx.len=inx.length;
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER,bufObj.inx);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,newUint16Array(inx),gl.STATIC_DRAW);
gl.enableVertexAttribArray(progDraw.inPos);
gl.vertexAttribPointer(progDraw.inPos,2,gl.FLOAT,false,0,0);
gl.enable(gl.DEPTH_TEST);
gl.clearColor(0.0,0.0,0.0,1.0);
window.onresize=resize;
resize();
requestAnimationFrame(render);
}
functionresize(){
//vp_size=[gl.drawingBufferWidth,gl.drawingBufferHeight];
vp_size=[window.innerWidth,window.innerHeight];
//vp_size=[256,256]
canvas.width=vp_size[0];
canvas.height=vp_size[1];
}
functionrender(deltaMS){
gl.viewport(0,0,canvas.width,canvas.height);
gl.clear(gl.COLOR_BUFFER_BIT|gl.DEPTH_BUFFER_BIT);
gl.uniform1f(progDraw.minX,-2.5);
gl.uniform1f(progDraw.minY,-2.0);
gl.uniform1f(progDraw.maxX,1.5);
gl.uniform1f(progDraw.maxY,2.0);
gl.uniform2f(progDraw.viewportDimensions,canvas.width,canvas.height);
gl.drawElements(gl.TRIANGLES,bufObj.inx.len,gl.UNSIGNED_SHORT,0);
requestAnimationFrame(render);
}
initScene();
})();
html,body{margin:0;overflow:hidden;}
precisionmediumpfloat;
attributevec2inPos;
voidmain()
{
gl_Position=vec4(inPos.xy,0.0,1.0);
}
precisionmediumpfloat;
uniformvec2viewportDimensions;
uniformfloatminX;
uniformfloatmaxX;
uniformfloatminY;
uniformfloatmaxY;
vec3hsv2rgb(vec3c){
vec4K=vec4(1.0,2.0/3.0,1.0/3.0,3.0);
vec3p=abs(fract(c.xxx+K.xyz)*6.0-K.www);
returnc.z*mix(K.xxx,clamp(p-K.xxx,0.0,1.0),c.y);
}
voidmain()
{
floatx=gl_FragCoord.x;
floaty=gl_FragCoord.y;
vec2c=mix(vec2(minX,minY),vec2(maxX,maxY),gl_FragCoord.xy/viewportDimensions.xy);
vec2z=c;
floatlimit=64.0;
floatiterations=0.0;
for(inti=0;i<64;i++){
floatt=2.0*z.x*z.y+c.y;
z.x=z.x*z.x-z.y*z.y+c.x;
z.y=t;
if(z.x*z.x+z.y*z.y>4.0){
break;
}
iterations+=1.0;
}
floatitRGB=iterations/limit;
vec3hsv=vec3(itRGB,1.0,1.0);
vec3rgb=hsv2rgb(hsv);
gl_FragColor=vec4(rgb,1);
}
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editedMar24,2019at15:09
answeredMar24,2019at9:27
Rabbid76Rabbid76
176k2525goldbadges101101silverbadges145145bronzebadges
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mixisavector-wisefunction,soyoushouldusemix(vec2(minX,minY),vec2(maxX,maxY),gl_FragCoord.xy/viewportDimensions).
– NicolBolas
Mar24,2019at14:51
I'mnotsureifusingmixisreallythebestoption.Thetransformationinquestioncanbereducedtoasimplemultiply-add,andpre-calcultaingthe2coefficientsandsendingthosetotheshaderappearsmoreefficienttome
– derhass
Mar24,2019at14:54
1
@uhin:"IfIputgl_FragColor=vec4(gl_FragCoord.x,gl_FragCoord.y,1,1);itjustdisplaysawhitescreen,meaningthattherewouldbea1forboththexandy,foreveryfragment?Why?Thatiswhatisconfusingme."Butthatpointisexplicitelyaddressedintheanswer.Itdoesntmeanitis1,itmeansitis>=1,andthatishowitisupposedto.
– derhass
Mar24,2019at15:05
1
@derhassOH!Ithoughtthatthevaluesofgl_FragCoordwerefrom[0,1].Thanks!
– uhin
Mar24,2019at15:09
1
@Rabbid76myproblemwasthatIwassettingmyuniformsafterendingtheshaderprogram.Ifixeditnow.Thanks!
– uhin
Mar24,2019at15:16
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