Lecture 05: Culling. Depth buffer

Backface culling

[1]

“Backface culling” experiment

Deduction phase

• Check it out on the Cornell box obj
• What about performance?

“Backface culling” experiment

Experiment

Let’s implement it together

“Backface culling” experiment

What is the new knowledge?

• Triangle strips ordering

Order of rendering

Idea: sort all triangles from farthest to nearest from camera [2]

“Order of rendering” experiment

Deduction phase

• After transformations Z-coordinate is still exist
• Is it possible to sort triangle by Z to nearest triangles will cover farthest one’s?
• What about performance?

“Order of rendering” experiment

Experiment

Let’s implement it together

“Order of rendering” experiment

What is the new knowledge?

• Solves the ordering issue
• Requires preliminary sorting of triangles
• Exists more complex cases

Mixed-triangle case

Kliment Redko. Suprematism

Depth buffer

vector<color> frame_buffer;
vector<float> depth_buffer; //+Infs, for instance

void SetPixel(unsigned short x, unsigned short y, float z, color color)
{
    frame_buffer[y * width + x] = color;
    depth_buffer[y * width + x] = z;
}

[2]

Z-buffer culling

bool DepthTest(unsigned short x, unsigned short y, float z)
{
    return z < depth_buffer[y * width + x]; //Depends on Z-axis directions
}

void SetPixel(unsigned short x, unsigned short y, float z, color color)
{
    if (DepthTest(x, y, z))
    {
        frame_buffer[y * width + x] = color;
        depth_buffer[y * width + x] = z;
    }
}

[2]

“Z-buffer culling” experiment

Deduction phase

• Possible to skip SetPixel if depth test fails
• What about performance?

“Z-buffer culling” experiment

Experiment

Let’s implement it together

“Z-buffer culling” experiment

Reference

“Z-buffer culling” experiment

What is the new knowledge?

• Z-buffer culling solves hard cases