I am working on volumetric raycasting and I am having a hard time finding the way to calculate the step size so that every step, the ray would step to a new voxel in my fragment shader GLSL.
I have a 3D box of dimension which doesn't have equal dimension on all side (x,y,z) and I already have that value and I also have a vec3 ray direction.
I need to know the step size for the ray or normalized ray to traverse from the starting and end of the hitting point in the cube.
From the axis-aligned box intersection, I know the tmin and tmax.
I know the code of AABI is irrelevant but I am adding this for any reference if needed.
vec2 boxIntersection(vec3 ray_direction2, float origin[3]){
float boxmin[3] = float[3](0.0, 0.0, 0.0);
float boxmax[3] = float[3](1.0, 1.0, 1.0);
vec3 invdir = 1.0/ray_direction2;
float inv_raydirection[3] = float[3](invdir.x, invdir.y, invdir.z);
for(int i=0; i<3; i++ ){
float t1 = (boxmin[i]-origin[i])*inv_raydirection[i];
float t2 = (boxmax[i]-origin[i])*inv_raydirection[i];
tmin = min(tmin, min(t1, t2));
tmax = max(tmax, max(t1, t2));
if(tmax>max(tmin,0.0)){
return vec2(tmin, tmax);
}
else{
discard;
}
}
Related
I've been trying to learn screen-space techniques, specifically Ray-marching ones but I have been struggling to get a single working example to continue learning from and solidify my knowledge. I'm implementing Screen-space shadows following this article but my result just seems to be a white image and I cannot seem to understand why. The code makes sense to me but the result does not seem to be right. I can't seem to understand where I might have gone wrong while attempting this screen-space ray-marching technique and would appreciate any insight to that will help me continue learning.
Using Vulkan + GLSL
Full shader: screen_space_shadows.glsl
// calculate screen space shadows
float computeScreenSpaceShadow()
{
vec3 FragPos = texture(gPosition, uvCoords).rgb;
vec4 ViewSpaceLightPosition = camera.view * light.LightPosition;
vec3 LightDirection = ViewSpaceLightPosition.xyz - FragPos.xyz;
// Ray position and direction in view-space.
vec3 RayPos = texture(gPosition, uvCoords).xyz; // ray start position
vec3 RayDirection = normalize(-LightDirection.xyz);
// Save original depth of the position
float DepthOriginal = RayPos.z;
// Ray step
vec3 RayStep = RayDirection * STEP_LENGTH;
float occlusion = 0.0;
for(uint i = 0; i < MAX_STEPS; i++)
{
RayPos += RayStep;
vec2 Ray_UV = ViewToScreen(RayPos);
// Make sure the UV is inside screen-space
if(!ValidRay(Ray_UV)){
return 1.0;
}
// Compute difference between ray and cameras depth
float DepthZ = linearize_depth(texture(depthMap, Ray_UV).x);
float DepthDelta = RayPos.z - DepthZ;
// Check if camera cannot see the ray. Ray depth must be larger than camera depth = positive delta
bool canCameraSeeRay = (DepthDelta > 0.0) && (DepthDelta < THICKNESS);
bool occludedByOriginalPixel = abs(RayPos.z - DepthOriginal) < MAX_DELTA_FROM_ORIGINAL_DEPTH;
if(canCameraSeeRay && occludedByOriginalPixel)
{
// Mark as occluded
occlusion = 1.0;
break;
}
}
return 1.0 - occlusion;
}
Output
I have a Three js scene that contains a 100x100 plane centred at the origin (ie. min coord: (-50,-50), max coord: (50,50)). I am trying to have the plane appear as a colour wheel by using the x and z coords in a custom glsl shader. Using this guide (see HSB in polar coordinates, towards the bottom of the page) I have gotten my
Shader Code with Three.js Scene
but it is not quite right.
I have played around tweaking all the variables that make sense to me, but as you can see in the screenshot the colours change twice as often as what they should. My math intuition says just divide the angle by 2 but when I tried that it was completely incorrect.
I know the solution is very simple but I have tried for a couple hours and I haven't got it.
How do I turn my shader that I currently have into one that makes exactly 1 full colour rotation in 2pi radians?
EDIT: here is the relevant shader code in plain text
varying vec3 vColor;
const float PI = 3.1415926535897932384626433832795;
uniform float delta;
uniform float scale;
uniform float size;
vec3 hsb2rgb( in vec3 c ){
vec3 rgb = clamp(abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),
6.0)-3.0)-1.0,
0.0,
1.0 );
rgb = rgb*rgb*(3.0-2.0*rgb);
return c.z * mix( vec3(1.0), rgb, c.y);
}
void main()
{
vec4 worldPosition = modelMatrix * vec4(position, 1.0);
float r = 0.875;
float g = 0.875;
float b = 0.875;
if (worldPosition.y > 0.06 || worldPosition.y < -0.06) {
vec2 toCenter = vec2(0.5) - vec2((worldPosition.z+50.0)/100.0, (worldPosition.x+50.0)/100.0);
float angle = atan(worldPosition.z/worldPosition.x);
float radius = length(toCenter) * 2.0;
vColor = hsb2rgb(vec3((angle/(PI))+0.5,radius,1.0));
} else {
vColor = vec3(r,g,b);
}
vec4 mvPosition = modelViewMatrix * vec4(position, 1.0);
gl_PointSize = size * (scale/length(mvPosition.xyz));
gl_Position = projectionMatrix * mvPosition;
}
I have discovered that the guide I was following was incorrect. I wasn't thinking about my math properly but I now know what the problem was.
atan has a range from -PI/2 to PI/2 which only accounts for half of a circle. When worldPosition.x is negative atan will not return the correct angle since it is out of range of the function. The angle needs to be adjusted based on what quadrant it is in the plane.
Q1: do nothing
Q2: add PI to the angle
Q3: add PI to the angle
Q4: add 2PI to the angle
After this normalize the angle (divide by 2PI) then pass it to the hsb2rgb function.
I'm trying to write a function in GLSL that returns the signed distance to a rectangle. The rectangle is axis-aligned. I feel a bit stuck; I just can't wrap my head around what I need to do to make it work.
The best I came up with is this:
float sdAxisAlignedRect(vec2 uv, vec2 tl, vec2 br)
{
// signed distances for x and y. these work fine.
float dx = max(tl.x - uv.x, uv.x - br.x);
float dy = max(tl.y - uv.y, uv.y - br.y);
dx = max(0.,dx);
dy = max(0.,dy);
return sqrt(dx*dx+dy*dy);
}
Which produces a rectangle that looks like:
The lines show distance from the rectangle. It works fine but ONLY for distances OUTSIDE the rectangle. Inside the rectangle the distance is a static 0..
How do I also get accurate distances inside the rectangle using a unified formula?
How about this...
float sdAxisAlignedRect(vec2 uv, vec2 tl, vec2 br)
{
vec2 d = max(tl-uv, uv-br);
return length(max(vec2(0.0), d)) + min(0.0, max(d.x, d.y));
}
Here's the result, where green marks a positive distance and red negative (code below):
Breakdown:
Get the signed distance from x and y borders. u - left and right - u are the two x axis distances. Taking the maximum of these values gives the signed distance to the closest border. Viewing d.x and d.y are shown individually in the images below.
Combine x and y:
If both values are negative, take the maximum (i.e. closest to a border). This is done with min(0.0, max(d.x, d.y)).
If only one value is positive, that's the distance we want.
If both values are positive, the closest point is a corner, in which case we want the length. This can be combined with the above case by taking the length anyway and making sure both values are positive: length(max(vec2(0.0), d)).
These two parts to the equation are mutually exclusive, i.e. only one will produce a non-zero value, and can be summed.
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
vec2 uv = fragCoord.xy / iResolution.xy;
uv -= 0.5;
uv *= vec2(iResolution.x/iResolution.y,1.0);
uv += 0.5;
float d = sdAxisAlignedRect(uv, vec2(0.3), vec2(0.7));
float m = 1.0 - abs(d)/0.1;
float s = sin(d*400.0) * 0.5 + 0.5;
fragColor = vec4(s*m*(-sign(d)*0.5+0.5),s*m*(sign(d)*0.5+0.5),0,1);
}
I'm trying to get a screen position of a vertex in pixels inside a vertex shader,
I saw some others posts here but I can't find answer that works for me.
this is what I've got in my vertex Shader:
#version 400
layout (location = 0) in vec3 inPosition;
uniform mat4 MVP; // modelViewProjection
uniform vec2 window;
void main()
{
// vertex in screen space
vec2 fake_frag_coord = (MVP * vec4(inPosition,1.0)).xy;
float X = (fake_frag_coord.x*window.x/2.0) + window.x;
float Y = (fake_frag_coord.y*window.y/2.0) + window.y;
}
It's not working very well and I know it's a strange think to do inside a vertex shader but I want to multiply my vertex offset by a 2d texture, so I need to find the pixel the vertex is on top to be able to multiply it by the pixel of the texture.
thanks!
Luiz
I have corrected your vertex shader with proper terms, and shown you the exact sequence of transformations that actually happens when GL computes gl_FragCoord (window-space).
#version 400
layout (location = 0) in vec4 inPosition; // Always use vec4, it makes life easier!
uniform mat4 MVP; // modelViewProjection
uniform vec2 window;
void main()
{
// Vertex in clip-space
vec4 fake_frag_coord = (MVP * inPosition); // Range: [-w,w]^4
// Vertex in NDC-space
fake_frag_coord.xyz /= fake_frag_coord.w; // Rescale: [-1,1]^3
fake_frag_coord.w = 1.0 / fake_frag_coord.w; // Invert W
// Vertex in window-space
fake_frag_coord.xyz *= vec3 (0.5) + vec3 (0.5); // Rescale: [0,1]^3
fake_frag_coord.xy *= window; // Scale and Bias for Viewport
// Assume depth range: [0,1] --> No need to adjust fake_frag_coord.z
[...]
}
Texture coordinates and window-space coordinates are very different things, however. Generally you need normalized coordinates for traditional texture fetches, that means you want the coordinates in the range [0,1].
Luckily window-space and texture-space share the same origin convention (0,0) = bottom-left, so you can cut out the line below to get the appropriate texture coordinates:
fake_frag_coord.xy *= window; // Scale and Bias for Viewport
I think Andon M. Coleman's answer is fine. However, I like to point out a more general issue with the approach discussed in the question: there might be no meaningful screen space position for a vertex at all.
The vertex might lie utside the viewing frustum. This will not be a a problem if the vertices you draw are guaranteed to lie in the frustum, or if you are drawing only points.
But it will fail if you have primitives intersecting the near plane. You might think that in such a case, you just get some coordinates which are outside [-1,1] in NDC space, and if you just use them to assign some output value for the vertex, the clipping state will make it right. But that assumption is wrong. You might values which are pefectly in [-1,1] in NDC space even for vertices which are outside the frustum, and it it will appear as if the vertices lie in front of the camera for all vertices wich actually lie behind the camera. And no subsequent clipping stage is able to fix this.
The only way to get this right would be to actually carry out the clipping operation, before doing the divide by w. And this is something you don't want to do in a vertex shader.
If you want to get this working on the js part of things, this is how I adapted Andon M. Coleman's reply:
var winW = window.innerWidth;
var winH = window.innerHeight;
camera.updateProjectionMatrix();
// Not sure about the order of these! I was using orthographic camera so it didn't matter but double check the order if it doesn't work!
var MVP = camera.projectionMatrix.multiply(camera.matrixWorldInverse);
// position to vertex clip-space
var fake_frag_coord = position.applyMatrix4(MVP); // Range: [-w,w]^4
// vertex to NDC-space
fake_frag_coord.x = fake_frag_coord.x / fake_frag_coord.w; // Rescale: [-1,1]^3
fake_frag_coord.y = fake_frag_coord.y / fake_frag_coord.w; // Rescale: [-1,1]^3
fake_frag_coord.z = fake_frag_coord.z / fake_frag_coord.w; // Rescale: [-1,1]^3
fake_frag_coord.w = 1.0 / fake_frag_coord.w; // Invert W
// Vertex in window-space
fake_frag_coord.x = fake_frag_coord.x * 0.5;
fake_frag_coord.y = fake_frag_coord.y * 0.5;
fake_frag_coord.z = fake_frag_coord.z * 0.5;
fake_frag_coord.x = fake_frag_coord.x + 0.5;
fake_frag_coord.y = fake_frag_coord.y + 0.5;
fake_frag_coord.z = fake_frag_coord.z + 0.5;
// Scale and Bias for Viewport (We want the window coordinates, so no need for this)
fake_frag_coord.x = fake_frag_coord.x / winW;
fake_frag_coord.y = fake_frag_coord.y / winH;
I am working with OpenGL ES 2.0 on an Android device.
I am trying to get a sphere up and running and drawing. Currentley, I almost have a sphere, but clearly it's being done very, very wrong.
In my app, I hold a list of Vector3's, which I convert to a ByteBuffer along the way, and pass to OpenGL.
I know my code is okay, since I have a Cube and Tetrahedron drawing nicley.
What two parts I changed were:
Determing the vertices
Drawing the vertices.
Here are the code snippits in question. What am I doing wrong?
Determining the polar coordinates:
private void ConstructPositionVertices()
{
for (float latitutde = 0.0f; latitutde < (float)(Math.PI * 2.0f); latitutde += 0.1f)
{
for (float longitude = 0.0f; longitude < (float)(2.0f * Math.PI); longitude += 0.1f)
{
mPositionVertices.add(ConvertFromSphericalToCartesian(1.0f, latitutde, longitude));
}
}
}
Converting from Polar to Cartesian:
public static Vector3 ConvertFromSphericalToCartesian(float inLength, float inPhi, float inTheta)
{
float x = inLength * (float)(Math.sin(inPhi) * Math.cos(inTheta));
float y = inLength * (float)(Math.sin(inPhi) * Math.sin(inTheta));
float z = inLength * (float)Math.cos(inTheta);
Vector3 convertedVector = new Vector3(x, y, z);
return convertedVector;
}
Drawing the circle:
inGL.glDrawArrays(GL10.GL_TRIANGLES, 0, numVertices);
Obviously I omitted some code, but I am positive my mistake lies in these snippits somewhere.
I do nothing more with the points than pass them to OpenGL, then call Triangles, which should connect the points for me.. right?
EDIT:
A picture might be nice!
your z must be calculated using phi. float z = inLength * (float)Math.cos(inPhi);
Also,the points generated are not triangles so it would be better to use GL_LINE_STRIP
Using triangle strip on Polar sphere is as easy as drawing points in pairs, for example:
const float GL_PI = 3.141592f;
GLfloat x, y, z, alpha, beta; // Storage for coordinates and angles
GLfloat radius = 60.0f;
const int gradation = 20;
for (alpha = 0.0; alpha < GL_PI; alpha += GL_PI/gradation)
{
glBegin(GL_TRIANGLE_STRIP);
for (beta = 0.0; beta < 2.01*GL_PI; beta += GL_PI/gradation)
{
x = radius*cos(beta)*sin(alpha);
y = radius*sin(beta)*sin(alpha);
z = radius*cos(alpha);
glVertex3f(x, y, z);
x = radius*cos(beta)*sin(alpha + GL_PI/gradation);
y = radius*sin(beta)*sin(alpha + GL_PI/gradation);
z = radius*cos(alpha + GL_PI/gradation);
glVertex3f(x, y, z);
}
glEnd();
}
First point entered is as follows the formula, and the second one is shifted by the single step of alpha angle (from the next parallel).