Jump to content
• Advertisement

# OpenGL Sub-surface scattering hack ( comments wanted! )

This topic is 3783 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

## Recommended Posts

I was fiddling around in FX Composer last night and came up with a pretty nice-looking fake sub-surface scattering effect, as follows: http://img131.imageshack.us/img131/1489/sss1je8.jpg http://img131.imageshack.us/img131/2131/sss2tt2.jpg http://img131.imageshack.us/img131/3440/sss3gu5.jpg http://img141.imageshack.us/img141/3603/sss4nu5.jpg I'll post my full algorithm/code when I get back from work later today. In a nutshell, I have a simple half-lambert base diffuse term, nothing special. The sub-surface scattering effect is divided up into three parts: 1) A dot product between the inverse surface normal and the light, clamped from 0 to 1, and finally distance attenuated; 2) Another half-lambert term between the inverse normal and view, also distance attenuated; 3) Scaling of subsurface color by red, green and blue extinction coefficients. The final shot demonstrates the effects of tweaking these to produce a blue scatter color. In addition, I have the 1 - N dot V squared rim lighting term put forth in the Dawn demo by nVidia (but this time scaled by the clamped dot product between light and normal, to avoid that weird backlighting) and a basic Blinn-Phong specular added on top. Since those pictures were taken I've done some basic work on extending my algorithm to account for colored lighting and non-uniform material thickness, although it doesn't look quite as nice as it does in those earlier screens. So, my questions are: 1) Anyone know of a good way to make this handle the non-uniform thickness more gracefully (I'll post some pictures later for review) 2) Any additonal suggestions for improving this to look more skin-like as a whole? Feedback of any sort is appreciated, though. I originally wrote this to replace some shaders in Oblivion and possibly even Doom 3, and as such lack the ability to use depth buffers, spherical harmonics or any of that stuff, unless any and all information can be passed in through textures and shader constants ONLY. This is also targeted at SM3.0, although it works just fine in SM2.0 and the OpenGL equivalents (this has been ported to ARB assembly without incident)

#### Share this post

##### Share on other sites
Advertisement
Alright, that took decidedly longer than expected to post-- that's what you get for being busy, I guess :(

Anyways, here's a shot with the translucency map and a few tweaks:
http://img143.imageshack.us/img143/2391/sssab9.jpg

I obviously fixed the eyebrow and hair thing, but it looks less... soft. Any suggestions? Should I even bother posting the code?

#### Share this post

##### Share on other sites
For being so simple, these screenies look quite impressive. I'd certainly love to see that fx/fxproj to play with it :)

I only miss a little rougness (pores) and some more oilyness (specular) to be convinced that this is skin. But again, for being a quite simple approximation, this already looks awesome.

To address the thickness problem, maybe xNormal can help? That tool supports among many other things producing a thickness map. Having thickness from every point of view as shader input, the wrong lighting visible on the ear in the last shot should disappear.
One could also overlay two thickness maps, to account for bones (this would need another model for the skull to be created, but I guess that wouldn't be too hard to derive from the original mesh - it doesn't have to be perfect). This would make the head in the last shot look less like an obsidian statue and more like a flesh and bone thing (well, if red was used for scattering).

#### Share this post

##### Share on other sites
Code isn't a problem, here's all the relevant shader stuff
string description = "Subsurface Scattering Hack";//------------------------------------float4x4 worldViewProj : WorldViewProjection;float4x4 world   : World;float4x4 worldInverseTranspose : WorldInverseTranspose;float4x4 viewInverse : ViewInverse;float4 LightPosition1 : POSITION<	string Object = "PointLight";	string UIName =  "Light 1";	string Space = "World";> 	= {1403.0f, 1441.0f, 1690.0f, 0.0f};float3 specColor<	string UIWidget = "color";	string UIName = "Specular Color";> = {0.9f, 0.9f, 1.0f};float3 lightColor<	string UIWidget = "color";	string UIName = "Light Color";> = {1.0f, 1.0f, 1.0f};float materialThickness<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Material Thickness Factor";> 	= 0.6f;float rimScalar<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Rim Light Strength";> 	= 1.0f;float extinctionCoefficientRed<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Red";> 	= 0.80f;float extinctionCoefficientBlue<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Blue";> 	= 0.12f;float extinctionCoefficientGreen<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Green";> 	= 0.20f;float specularPower<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 100.0f;	float UIStep = 0.50f;	string UIName = "Blinn Specular Power";> = 1.0f;texture diffuseTex;texture thicknessTex;texture normalTex;sampler normalSampler = sampler_state{	texture		= <normalTex>;	MinFilter	=	point;	MagFilter	=	point;	MipFilter	=	point;	AddressU	=	CLAMP;	AddressV	=	CLAMP;};sampler2D diffuseSampler = sampler_state{	Texture		=	<diffuseTex>;	MinFilter	=	Linear;	MagFilter	=	Linear;	MipFilter	=	Linear;	AddressU	=	WRAP;	AddressV	=	WRAP;};sampler2D thicknessSampler = sampler_state{	Texture		=	<diffuseTex>;	MinFilter	=	Linear;	MagFilter	=	Linear;	MipFilter	=	Linear;	AddressU	=	WRAP;	AddressV	=	WRAP;};struct VSOut{	float4 position			:	POSITION;	float2 texCoord			:	TEXCOORD0;	float3 worldNormal		:	TEXCOORD1;	float3 eyeVec     		:	TEXCOORD2;	float3 lightVec			:	TEXCOORD3;	float3 worldTangent		: 	TEXCOORD4;	float3 worldBinormal		: 	TEXCOORD5;	float3 vertPos			:	TEXCOORD6;};struct AppData {   	float4 position	:	POSITION;	float2 UV	:	TEXCOORD0;	float3 normal	:	NORMAL;	float3 tangent	: 	TANGENT;	float3 binormal	: 	BINORMAL;};VSOut SkinVS(AppData IN, uniform float4 lightPosition){	VSOut OUT;	OUT.worldNormal = normalize(mul(IN.normal, worldInverseTranspose).xyz);	OUT.worldTangent = normalize(mul(IN.tangent, worldInverseTranspose).xyz);	OUT.worldBinormal = normalize(mul(IN.binormal, worldInverseTranspose).xyz);	 	float3 worldSpacePos = mul(IN.position, world);	OUT.lightVec = lightPosition - worldSpacePos;	OUT.texCoord = IN.UV;	OUT.eyeVec = viewInverse[3].xyz - worldSpacePos;	OUT.position = mul(IN.position, worldViewProj);	OUT.vertPos = worldSpacePos;	return OUT;};float halfLambert(float3 vec1, float3 vec2){	float product = dot(vec1, vec2);	product *= 0.5;	product += 0.5;	return product;}float blinnPhongSpecular(float3 normalVec, float3 lightVec, float specPower){	float3 halfAngle = normalize(normalVec + lightVec);	return pow(saturate(dot(normalVec, halfAngle)), specPower);}float4 SkinPS(VSOut IN) : COLOR0{	float attenuation = (1.0f/distance(LightPosition1, IN.vertPos));	attenuation *= 10.0f;	float3 eyeVec 	= normalize(IN.eyeVec);	float3 lightVec = normalize(IN.lightVec.xyz);	float3 worldNormal = normalize(IN.worldNormal);	//float3 nMap = tex2D(normalSampler, IN.texCoord);	//worldNormal.x = dot(nMap.x, IN.worldTangent);	//worldNormal.y = dot(nMap.y, IN.worldBinormal);	//worldNormal.z = dot(nMap.z, IN.worldNormal);	float4 dotLN	= halfLambert(lightVec, worldNormal) * attenuation;	float3 indirectLightComponent = (float3)(materialThickness * max(0, dot(-worldNormal, lightVec)));	indirectLightComponent += materialThickness * halfLambert(-eyeVec, lightVec);	indirectLightComponent *= attenuation;	indirectLightComponent.r *= extinctionCoefficientRed;	indirectLightComponent.g *= extinctionCoefficientGreen;	indirectLightComponent.b *= extinctionCoefficientBlue;	indirectLightComponent.rgb *= tex2D(thicknessSampler, IN.texCoord).r;	float3 rim = (float3)(1.0f - max(0.0f, dot(worldNormal, eyeVec)));	rim *= rim;	dotLN *= tex2D(diffuseSampler, IN.texCoord);	float4 finalCol = dotLN + float4(indirectLightComponent, 1.0f);	rim *= max(0.0f, dot(worldNormal, lightVec)) * specColor;	finalCol.rgb += (rim * rimScalar * attenuation * finalCol.a);	finalCol.rgb += (blinnPhongSpecular(worldNormal, lightVec, specularPower) * attenuation * specColor * finalCol.a * 0.05f);	finalCol.rgb *= lightColor;	return float4(finalCol);};technique subSurfaceScattering{    pass p0     {				VertexShader		= compile vs_2_0 SkinVS(LightPosition1);		PixelShader			= compile ps_2_0 SkinPS();		ZEnable 			= true;		ZWriteEnable 		= true;		AlphaBlendEnable	= false;		SrcBlend 			= SrcAlpha;		DestBlend 			= InvSrcAlpha;		CullMode 			= CW; //None, CW, or CCW    }}

That's regular HLSL, could be converted to Cg, GLSL or whatever other shading language you prefer. I just use the Dawn lambert skin fxproj and apply that skin shader to the face. I made the thickness map myself, as you can see it's pretty hack-y, so I'll leave you be on that. Diffuse map comes with FX Composer.

Thanks for the tips! :) I'm working on a normal map thing as we speak, although the ones supplied with the Dawn demo just look kind of funny when I apply them-- perhaps they're in the wrong space or something.

#### Share this post

##### Share on other sites
Thanks for the shader code, InvalidPointer. Unluckily, it'll take some work this weekend to get it to work, since FX Composer doesn't like something, it crashes right away :(

I've been thinking about thickness and all for a while, there seems to be no easy way to get it perfect everywhere. Even a thickness map won't do, because no matter how you turn it, the ears will always be shaded wrong. There's of course the option to calculate per-pixel thicknes like in nVidia's "Luna" demo, but then we're not talking about a fast and efficient implementation any more (render several passes, blur, etc...). Also, the algorithm again is only an approximation. Mostly it doesn't matter much, but for example looking at the oral cavity from the side, it will produce a false "thick" result, when in fact it's mostly "empty" air with two thin layers of cheeks.

So, I was wondering if shadow mapping the skull wouldn't be helpful, and still cheap enough (a single z-only render of a possibly much simplified model).
The idea is to scale the head model down a bit, and remove/flatten ears and nose and render that into the shadow map. It probably doesn't even have to be perfectly anatomically accurate.
So that will leave you with an "outer part" where there is skin and flesh (and rim light scattering), and an "inner part" where bones absorb all of the back light (regardless of thickness), so only scattering from incidential light and half-lambert lighting account to the colour.

Thickness should not be something to worry about much then. Around the border, anything N dot V isn't a terribly bad approximation, since the normals will point more "sidewards" the thinner the cross-section.
Now, in the "deeper" regions it does not work so well, but we have these masked out with the shadow map. Also, the disturbing artefacts when the ear is rim-lit although it obviously couldn't be (as the head is in the way) are gone.

#### Share this post

##### Share on other sites
Quote:
 Original post by samothThanks for the shader code, InvalidPointer. Unluckily, it'll take some work this weekend to get it to work, since FX Composer doesn't like something, it crashes right away :(I've been thinking about thickness and all for a while, there seems to be no easy way to get it perfect everywhere. Even a thickness map won't do, because no matter how you turn it, the ears will always be shaded wrong. There's of course the option to calculate per-pixel thicknes like in nVidia's "Luna" demo, but then we're not talking about a fast and efficient implementation any more (render several passes, blur, etc...). Also, the algorithm again is only an approximation. Mostly it doesn't matter much, but for example looking at the oral cavity from the side, it will produce a false "thick" result, when in fact it's mostly "empty" air with two thin layers of cheeks.So, I was wondering if shadow mapping the skull wouldn't be helpful, and still cheap enough (a single z-only render of a possibly much simplified model).The idea is to scale the head model down a bit, and remove/flatten ears and nose and render that into the shadow map. It probably doesn't even have to be perfectly anatomically accurate.So that will leave you with an "outer part" where there is skin and flesh (and rim light scattering), and an "inner part" where bones absorb all of the back light (regardless of thickness), so only scattering from incidential light and half-lambert lighting account to the colour.Thickness should not be something to worry about much then. Around the border, anything N dot V isn't a terribly bad approximation, since the normals will point more "sidewards" the thinner the cross-section.Now, in the "deeper" regions it does not work so well, but we have these masked out with the shadow map. Also, the disturbing artefacts when the ear is rim-lit although it obviously couldn't be (as the head is in the way) are gone.

Could the thickness map not be tweaked? I can use XNormal with some settings fiddles to make a decent thickness thing and then just work in Photoshop to make a nice-looking approximation for some of the effects you describe.

#### Share this post

##### Share on other sites

• Advertisement

### Announcements

• Advertisement

• ### Similar Content

• By nOoNEE
i am reading this book : link
in the OpenGL Rendering Pipeline section there is a picture like this: link
but the question is this i dont really understand why it is necessary to turn pixel data in to fragment and then fragment into pixel could please give me a source or a clear Explanation that why it is necessary ? thank you so mu

• By Inbar_xz
I'm using the OPENGL with eclipse+JOGL.
My goal is to create movement of the camera and the player.
I create main class, which create some box in 3D and hold
an object of PlayerAxis.
I create PlayerAxis class which hold the axis of the player.
If we want to move the camera, then in the main class I call to
the func "cameraMove"(from PlayerAxis) and it update the player axis.
That's work good.
The problem start if I move the camera on 2 axis,
for example if I move with the camera right(that's on the y axis)
and then down(on the x axis) -
in some point the move front is not to the front anymore..
In order to move to the front, I do
player.playerMoving(0, 0, 1);
And I learn that in order to keep the front move,
I need to convert (0, 0, 1) to the player axis, and then add this.
I think I dont do the convert right..
I will be glad for help!

Here is part of my PlayerAxis class:

//player coordinate float x[] = new float[3]; float y[] = new float[3]; float z[] = new float[3]; public PlayerAxis(float move_step, float angle_move) { x[0] = 1; y[1] = 1﻿; z[2] = -1; step = move_step; angle = angle_move; setTransMatrix(); } public void cameraMoving(float angle_step, String axis) { float[] new_x = x; float[] new_y = y; float[] new_z = z; float alfa = angle_step * angle; switch(axis) { case "x": new_z = addVectors(multScalar(z, COS(alfa)), multScalar(y, SIN(alfa))); new_y = subVectors(multScalar(y, COS(alfa)), multScalar(z, SIN(alfa))); break; case "y": new_x = addVectors(multScalar(x, COS(alfa)), multScalar(z, SIN(alfa))); new_z = subVectors(multScalar(z, COS(alfa)), multScalar(x, SIN(alfa))); break; case "z": new_x = addVectors(multScalar(x, COS(alfa)), multScalar(y, SIN(alfa))); new_y = subVectors(multScalar(y, COS(alfa)), multScalar(x, SIN(alfa))); }﻿ x = new_x; y = new_y; z = new_z; normalization(); } public void playerMoving(float x_move, float y_move, float z_move) { float[] move = new float[3]; move[0] = x_move; move[1] = y_move; move[2] = z_move; setTransMatrix(); float[] trans_move = transVector(move); position[0] = position[0] + step*trans_move[0]; position[1] = position[1] + step*trans_move[1]; position[2] = position[2] + step*trans_move[2]; } public void setTransMat﻿rix() { for (int i = 0; i < 3; i++) { coordiTrans[0][i] = x[i]; coordiTrans[1][i] = y[i]; ﻿coordiTrans[2][i] = z[i]; } } public float[] transVector(float[] v) { return multiplyMatrixInVector(coordiTrans, v); }
and in the main class i have this:

public void keyPressed(KeyEvent e) { if (e.getKeyCode()== KeyEvent.VK_ESCAPE) { System.exit(0); //player move } else if (e.getKeyCode()== KeyEvent.VK_W) { //front //moveAmount[2] += -0.1f; player.playerMoving(0, 0, 1); } else if (e.getKeyCode()== KeyEvent.VK_S) { //back //moveAmount[2] += 0.1f; player.playerMoving(0, 0, -1); } else if (e.getKeyCode()== KeyEvent.VK_A) { //left //moveAmount[0] += -0.1f; player.playerMoving(-1, 0, 0); } else if (e.getKeyCode()== KeyEvent.VK_D) { //right //moveAmount[0] += 0.1f; player.playerMoving(1, 0, 0); } else if (e.getKeyCode()== KeyEvent.VK_E) { //moveAmount[0] += 0.1f; player.playerMoving(0, 1, 0); } else if (e.getKeyCode()== KeyEvent.VK_Q) { //moveAmount[0] += 0.1f; player.playerMoving(0, -1, 0); //camera move } else if (e.getKeyCode()== KeyEvent.VK_I) { //up player.cameraMoving(1, "x"); } else if (e.getKeyCode()== KeyEvent.VK_K) { //down player.cameraMoving(-1, "x"); } else if (e.getKeyCode()== KeyEvent.VK_L) { //right player.cameraMoving(-1, "y"); } else if (e.getKeyCode()== KeyEvent.VK_J) { //left player.cameraMoving(1, "y"); } else if (e.getKeyCode()== KeyEvent.VK_O) { //right round player.cameraMoving(-1, "z"); } else if (e.getKeyCode()== KeyEvent.VK_U) { //left round player.cameraMoving(1, "z"); } }
finallt found it.... i confused with the transformation matrix row and col. thanks anyway!
• By Lewa
So, i'm currently trying to implement an SSAO shader from THIS tutorial and i'm running into a few issues here.
Now, this SSAO method requires view space positions and normals. I'm storing the normals in my deferred renderer in world-space so i had to do a conversion and reconstruct the position from the depth buffer.
And something there goes horribly wrong (which has probably to do with worldspace to viewspace transformations).
(here is the full shader source code if someone wants to take a look at it)
Now, i suspect that the normals are the culprit.
vec3 normal = ((uNormalViewMatrix*vec4(normalize(texture2D(sNormals, vTexcoord).rgb),1.0)).xyz); "sNormals" is a 2D texture which stores the normals in world space in a RGB FP16 buffer.
Now i can't use the camera viewspace matrix to transform the normals into viewspace as the cameras position isn't set at (0,0,0), thus skewing the result.
So what i did is to create a new viewmatrix specifically for this normal without the position at vec3(0,0,0);
//"camera" is the camera which was used for rendering the normal buffer renderer.setUniform4m(ressources->shaderSSAO->getUniform("uNormalViewMatrix"), glmExt::createViewMatrix(glm::vec3(0,0,0),camera.getForward(),camera.getUp())//parameters are (position,forwardVector,upVector) ); Though i have the feeling this is the wrong approach. Is this right or is there a better/correct way of transforming a world space normal into viewspace?

• Hi,
I'm trying mix two textures using own shader system, but I have a problem (I think) with uniforms.
Code: https://github.com/HawkDeath/shader/tree/test
To debug I use RenderDocs, but I did not receive good results. In the first attachment is my result, in the second attachment is what should be.
PS. I base on this tutorial https://learnopengl.com/Getting-started/Textures.

• I'm having issues loading textures, as I'm clueless on how to handle / load images maybe I missing something, but the past few days I just google a lot to try to find a solution. Well theres two issues I think, one I'm using Kotlin Native (EAP) and OpenGL wrapper / STB image, so I'm not quite sure wheres the issue, if someone with more experience could give me some hints on how to solve this issue?
The code is here, if I'm not mistaken the workflow is pretty straight forward, stbi_load returns the pixels of the image (as char array or byte array) and you need to pass those pixels directly to glTexImage2D, so a I'm missing something here it seems.
Regards

• I've noticed in most post processing tutorials several shaders are used one after another: one for bloom, another for contrast, and so on. For example:
postprocessing.quad.bind() // Effect 1 effect1.shader.bind(); postprocessing.texture.bind(); postprocessing.quad.draw(); postprocessing.texture.unbind(); effect1.shader.unbind(); // Effect 2 effect2.shader.bind(); // ...and so on postprocessing.quad.unbind() Is this good practice, how many shaders can I bind and unbind before I hit performance issues? I'm afraid I don't know what the good practices are in open/webGL regarding binding and unbinding resources.
I'm guessing binding many shaders at post processing is okay since the scene has already been updated and I'm just working on a quad and texture at that moment. Or is it more optimal to put shader code in chunks and bind less frequently? I'd love to use several shaders at post though.
Another example of what I'm doing at the moment:
1) Loop through GameObjects, bind its phong shader (send color, shadow, spec, normal samplers), unbind all.
2) At post: bind post processor quad, and loop/bind through different shader effects, and so on ...
Thanks all!

• void collision(int v) { collision_bug_one(0.0f, 10.0f); glutPostRedisplay(); glutTimerFunc(1000, collision, 0); } void coll_sprite() { if (board[0][0] == 1) { collision(0); flag[0][0] = 1; } } void erase_sprite() { if (flag[0][0] == 1) { glColor3f(0.0f, 0.0f, 0.0f); glBegin(GL_POLYGON); glVertex3f(0.0f, 10.0f, 0.0f); glVertex3f(0.0f, 9.0f, 0.0f); glVertex3f(1.0f, 9.0f, 0.0f); glVertex3f(1.0f, 10.0f, 0.0f); glEnd(); } } I am using glutTimerFunc to wait a small amount of time to display a collision sprite before I black out the sprite. unfortunately my code only blacks out the said sprite without drawing the collision sprite, I have done a great deal of research on the glutTimerFunc and  animation.
• By Lewa
So, i stumbled upon the topic of gamma correction.
https://learnopengl.com/Advanced-Lighting/Gamma-Correction
So from what i've been able to gather: (Please correct me if i'm wrong)
Old CRT monitors couldn't display color linearly, that's why gamma correction was nessecary. Modern LCD/LED monitors don't have this issue anymore but apply gamma correction anyway. (For compatibility reasons? Can this be disabled?) All games have to apply gamma correction? (unsure about that) All textures stored in file formats (.png for example) are essentially stored in SRGB color space (as what we see on the monitor is skewed due to gamma correction. So the pixel information is the same, the percieved colors are just wrong.) This makes textures loaded into the GL_RGB format non linear, thus all lighting calculations are wrong You have to always use the GL_SRGB format to gamma correct/linearise textures which are in SRGB format
Now, i'm kinda confused how to proceed with applying gamma correction in OpenGL.
First of, how can i check if my Monitor is applying gamma correction? I noticed in my monitor settings that my color format is set to "RGB" (can't modify it though.) I'm connected to my PC via a HDMI cable. I'm also using the full RGB range (0-255, not the 16 to ~240 range)

What i tried to do is to apply a gamma correction shader shown in the tutorial above which looks essentially like this: (it's a postprocess shader which is applied at the end of the renderpipeline)
vec3 gammaCorrection(vec3 color){ // gamma correction color = pow(color, vec3(1.0/2.2)); return color; } void main() { vec3 color; vec3 tex = texture2D(texture_diffuse, vTexcoord).rgb; color = gammaCorrection(tex); outputF = vec4(color,1.0f); } The results look like this:
No gamma correction:
With gamma correction:

The colors in the gamma corrected image look really wased out. (To the point that it's damn ugly. As if someone overlayed a white half transparent texture. I want the colors to pop.)
Do i have to change the textures from GL_RGB to GL_SRGB in order to gamma correct them in addition to applying the post process gamma correction shader? Do i have to do the same thing with all FBOs? Or is this washed out look the intended behaviour?

• Hi

I am trying to program shadow volumes and i stumbled upon an artifact which i can not find the cause for.
I generate the shadow volumes using a geometry shader with reversed extrusion (projecting the lightfacing triangles to infinity) and write the stencil buffer according to z-fail. The base of my code is the "lighting" chapter from learnopengl.com, where i extended the shader class to include geometry shader. I also modified the "lightingshader" to draw the ambient pass when "pass" is set to true and the diffuse/ specular pass when set to false. For easier testing i added a view controls to switch on/off the shadow volumes' color rendering or to change the cubes' position, i made the lightnumber controllable and changed the diffuse pass to render green for easier visualization of my problem.

The first picture shows the rendered scene for one point light, all cubes and the front cube's shadow volume is the only one created (intentional). Here, all is rendered as it should be with all lit areas green and all areas inside the shadow volume black (with the volume's sides blended over).

If i now turn on the shadow volumes for all the other cubes, we get a bit of a mess, but its also obvious that some areas that were in shadow before are now erroneously lit (for example the first cube to the right from the originaly shadow volumed cube). From my testing the areas erroneously lit are the ones where more than one shadow volume marks the area as shadowed.

To check if a wrong stencil buffer value caused this problem i decided to change the stencil function for the diffuse pass to only render if the stencil is equal to 2. As i repeated this approach with different values for the stencil function i found out that if i set the value equal to 1 or any other uneven value the lit and shadowed areas are inverted and if i set it to 0 or any other even value i get the results shown above.
This lead me to believe that the value and thus the stencil buffer values may be clamped to [0,1] which would also explain the artifact, because twice in shadow would equal in no shadow at all, but from what i found on the internet and from what i tested with
GLint stencilSize = 0; glGetFramebufferAttachmentParameteriv(GL_DRAW_FRAMEBUFFER, GL_STENCIL, GL_FRAMEBUFFER_ATTACHMENT_STENCIL_SIZE, &stencilSize); my stencilsize is 8 bit, which should be values within [0,255].
Does anyone know what might be the cause for this artifact or the confusing results with other stencil functions?

// [the following code includes all used gl* functions, other parts are due to readability partialy excluded] // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 4); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation // -------------------- GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL); if (window == NULL) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); glfwSetCursorPosCallback(window, mouse_callback); glfwSetScrollCallback(window, scroll_callback); // tell GLFW to capture our mouse glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED); // glad: load all OpenGL function pointers // --------------------------------------- if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // ==================================================================================================== // window and functions are set up // ==================================================================================================== // configure global opengl state // ----------------------------- glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); // build and compile our shader program [...] // set up vertex data (and buffer(s)) and configure vertex attributes [...] // shader configuration [...] // render loop // =========== while (!glfwWindowShouldClose(window)) { // input processing and fps calculation[...] // render // ------ glClearColor(0.1f, 0.1f, 0.1f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glDepthMask(GL_TRUE); //enable depth writing glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw ambient component into color and depth buffer view = camera.GetViewMatrix(); projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); // setting up lighting shader for ambient pass [...] // render the cubes glBindVertexArray(cubeVAO); for (unsigned int i = 0; i < 10; i++) { //position cube [...] glDrawArrays(GL_TRIANGLES, 0, 36); } //------------------------------------------------------------------------------------------------------------------------ glDepthMask(GL_FALSE); //disable depth writing glEnable(GL_BLEND); glBlendFunc(GL_ONE, GL_ONE); //additive blending glEnable(GL_STENCIL_TEST); //setting up shadowShader and lightingShader [...] for (int light = 0; light < lightsused; light++) { glDepthFunc(GL_LESS); glClear(GL_STENCIL_BUFFER_BIT); //configure stencil ops for front- and backface to write according to z-fail glStencilOpSeparate(GL_FRONT, GL_KEEP, GL_DECR_WRAP, GL_KEEP); //-1 for front-facing glStencilOpSeparate(GL_BACK, GL_KEEP, GL_INCR_WRAP, GL_KEEP); //+1 for back-facing glStencilFunc(GL_ALWAYS, 0, GL_TRUE); //stencil test always passes if(hidevolumes) glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); //disable writing to the color buffer glDisable(GL_CULL_FACE); glEnable(GL_DEPTH_CLAMP); //necessary to render SVs into infinity //draw SV------------------- shadowShader.use(); shadowShader.setInt("lightnr", light); int nr; if (onecaster) nr = 1; else nr = 10; for (int i = 0; i < nr; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } //-------------------------- glDisable(GL_DEPTH_CLAMP); glEnable(GL_CULL_FACE); glStencilFunc(GL_EQUAL, 0, GL_TRUE); //stencil test passes for ==0 so only for non shadowed areas glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); //keep stencil values for illumination glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); //enable writing to the color buffer glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw diffuse and specular pass lightingShader.use(); lightingShader.setInt("lightnr", light); // render the cubes for (unsigned int i = 0; i < 10; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } } glDisable(GL_BLEND); glDepthMask(GL_TRUE); //enable depth writing glDisable(GL_STENCIL_TEST); //------------------------------------------------------------------------------------------------------------------------ // also draw the lamp object(s) [...] // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) // ------------------------------------------------------------------------------- glfwSwapBuffers(window); glfwP } // optional: de-allocate all resources once they've outlived their purpose: // ------------------------------------------------------------------------ glDeleteVertexArrays(1, &cubeVAO); glDeleteVertexArrays(1, &lightVAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. // ------------------------------------------------------------------ glfwTerminate(); return 0;

• Hi,
i am self teaching me graphics and oo programming and came upon this:
My Window class creates an input handler instance, the glfw user pointer is redirected to that object and methods there do the input handling for keyboard and mouse. That works. Now as part of the input handling i have an orbiting camera that is controlled by mouse movement. GLFW_CURSOR_DISABLED is set as proposed in the glfw manual. The manual says that in this case the cursor is automagically reset to the window's center. But if i don't reset it manually with glfwSetCursorPos( center ) mouse values seem to add up until the scene is locked up.
Here are some code snippets, mostly standard from tutorials:
// EventHandler m_eventHandler = new EventHandler( this, glm::vec3( 0.0f, 5.0f, 0.0f ), glm::vec3( 0.0f, 1.0f, 0.0f ) ); glfwSetWindowUserPointer( m_window, m_eventHandler ); m_eventHandler->setCallbacks(); Creation of the input handler during window creation. For now, the camera is part of the input handler, hence the two vectors (position, up-vector).  In future i'll take that functionally out into an own class that inherits from the event handler.
void EventHandler::setCallbacks() { glfwSetCursorPosCallback( m_window->getWindow(), cursorPosCallback ); glfwSetKeyCallback( m_window->getWindow(), keyCallback ); glfwSetScrollCallback( m_window->getWindow(), scrollCallback ); glfwSetMouseButtonCallback( m_window->getWindow(), mouseButtonCallback ); } Set callbacks in the input handler.
// static void EventHandler::cursorPosCallback( GLFWwindow *w, double x, double y ) { EventHandler *c = reinterpret_cast<EventHandler *>( glfwGetWindowUserPointer( w ) ); c->onMouseMove( (float)x, (float)y ); } Example for the cursor pos callback redirection to a class method.
// virtual void EventHandler::onMouseMove( float x, float y ) { if( x != 0 || y != 0 ) { // @todo cursor should be set automatically, according to doc if( m_window->isCursorDisabled() ) glfwSetCursorPos( m_window->getWindow(), m_center.x, m_center.y ); // switch up/down because its more intuitive m_yaw += m_mouseSensitivity * ( m_center.x - x ); m_pitch += m_mouseSensitivity * ( m_center.y - y ); // to avoid locking if( m_pitch > 89.0f ) m_pitch = 89.0f; if( m_pitch < -89.0f ) m_pitch = -89.0f; // Update Front, Right and Up Vectors updateCameraVectors(); } } // onMouseMove() Mouse movement processor method. The interesting part is the manual reset of the mouse position that made the thing work ...
// straight line distance between the camera and look at point, here (0,0,0) float distance = glm::length( m_target - m_position ); // Calculate the camera position using the distance and angles float camX = distance * -std::sin( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); float camY = distance * -std::sin( glm::radians( m_pitch) ); float camZ = -distance * std::cos( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); // Set the camera position and perspective vectors m_position = glm::vec3( camX, camY, camZ ); m_front = glm::vec3( 0.0, 0.0, 0.0 ) - m_position; m_up = m_worldUp; m_right = glm::normalize( glm::cross( m_front, m_worldUp ) ); glm::lookAt( m_position, m_front, m_up ); Orbiting camera vectors calculation in updateCameraVectors().
Now, for my understanding, as the glfw manual explicitly states that if cursor is disabled then it is reset to the center, but my code only works if it is reset manually, i fear i am doing something wrong. It is not world moving (only if there is a world to render :-)), but somehow i am curious what i am missing.

I am not a professional programmer, just a hobbyist, so it may well be that i got something principally wrong :-)
And thanks for any hints and so ...

• Advertisement

• 35
• 12
• 10
• 9
• 9
• ### Forum Statistics

• Total Topics
631358
• Total Posts
2999530
×

## Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!