Sign in to follow this  

I want to align my bullet hole decal with the surface hit

This topic is 2058 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

HI, this is my first post and would appreciate any help.

[url="http://youtu.be/z4sNfcOxp1I"]Here's a video of the problem[/url]

I am using the particle system from the "Particles3D" XNA example. Currently the texture is always aligned with the camera. I want it to be aligned with the surface hit.

In the video I have displayed the location and normal of each collision.

The sample particle system has a lot of redundant code that I don't need for the bullet holes. For example I don't need the particles to move, rotate, change size or color.

The vertex shader input contains a float3, Velocity, that I could presumably replace with the normal.

in the ParticleVertexShader the output.Position is calculated in ComputeParticlePosition.

[CODE]
// Custom vertex shader animates particles entirely on the GPU.
VertexShaderOutput ParticleVertexShader(VertexShaderInput input)
{
VertexShaderOutput output;

// Compute the age of the particle.
float age = CurrentTime - input.Time;

// Apply a random factor to make different particles age at different rates.
age *= 1 + input.Random.x * DurationRandomness;

// Normalize the age into the range zero to one.
float normalizedAge = saturate(age / Duration);
// Compute the particle position, size, color, and rotation.
output.Position = ComputeParticlePosition(input.Position, input.Velocity,
age, normalizedAge);
float size = ComputeParticleSize(input.Random.y, normalizedAge);
float2x2 rotation = ComputeParticleRotation(input.Random.w, age);
output.Position.xy += mul(input.Corner, rotation) * size * ViewportScale;

output.Color = ComputeParticleColor(output.Position, input.Random.z, normalizedAge);
output.TextureCoordinate = (input.Corner + 1) / 2;

return output;
}
[/CODE]

Inside ComputeParticlePosition the position is multiplied by the view and projection matrix.

[CODE]
// Vertex shader helper for computing the position of a particle.
float4 ComputeParticlePosition(float3 position, float3 velocity,
float age, float normalizedAge)
{
float startVelocity = length(velocity);
// Work out how fast the particle should be moving at the end of its life,
// by applying a constant scaling factor to its starting velocity.
float endVelocity = startVelocity * EndVelocity;

// Our particles have constant acceleration, so given a starting velocity
// S and ending velocity E, at time T their velocity should be S + (E-S)*T.
// The particle position is the sum of this velocity over the range 0 to T.
// To compute the position directly, we must integrate the velocity
// equation. Integrating S + (E-S)*T for T produces S*T + (E-S)*T*T/2.
float velocityIntegral = startVelocity * normalizedAge +
(endVelocity - startVelocity) * normalizedAge *
normalizedAge / 2;

position += normalize(velocity) * velocityIntegral * Duration;

// Apply the gravitational force.
position += Gravity * age * normalizedAge;

// Apply the camera view and projection transforms.
return mul(mul(float4(position, 1), View), Projection);
}
[/CODE]

So in summary, I don't need most of this code, I have only included it so you see what is currently happening. The input velocity is zero.

How do I transform the position so that it aligns with the normal?

Any help or pointers would be great.

Share this post


Link to post
Share on other sites
[url="http://youtu.be/wvXSONjKdqk"]Here's a video of the problem fixed![/url]

I ditched the idea of using a trianglelist based particle system. Instead I use a quad model circular array. I can manipulate the matrix up vector using the normal of the surface hit.

Thanks for looking.

BTW: I think I should have posted this in the XNA section, sorry about that, I didn't realise till after posting.

Share this post


Link to post
Share on other sites

This topic is 2058 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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this