Texel

A texel (short for texture pixel) is the fundamental unit of a texture.

While a pixel represents a single point of color data on a 2D screen display, a texel represents a single point of color (or data, such as depth or normals) stored within a texture.

The term texel is used in shader programming and graphics APIs to distinguish texture pixels from the pixels that are ultimately drawn on the screen. A single screen pixel may be generated from one texel, multiple texels, or even a fraction of a texel depending on how the texture is scaled and transformed.

Sampling and Coordinates

In a fragment shader, you are rarely access texels by their raw integer array index. Instead, you retrieve them using a Sampler via UV coordinates (normalized floating-point numbers between 0.0 and 1.0).

For example, the following code retrieves a texel at UVs (0.25, 0.50) from a texture:

vec4 color = texture(TEXTURE, vec2(0.25, 0.50));

If the provided texture size was, for example, 200x200px, the operation would try to retrieve the pixel at coordinates (50, 100), and the resulting color variable would contain the color of that pixel.

What if I want the exact pixel coordinate?

To get the actual pixel coordinate, you can multiply the UV coordinates by the texture's dimensions:

vec2 pixelCoord = vec2(0.25, 0.50) * TEXTURE_PIXEL_SIZE;

This is almost never useful, but is provided here to help understand how UV coordinates map to pixel coordinates.

Depending on the texture's filtering settings configured in Godot, the hardware will handle texels in one of two primary ways during sampling:

• Nearest (Point) Filtering: The GPU grabs the exact single texel closest to the UV coordinate. This is the default mode for 2D pixel art games in Godot, resulting in sharp, hard edges when assets are scaled up.
• Linear / Linear Mipmap Filtering: The GPU samples the closest neighboring texels surrounding the UV coordinate and mathematically blends them together.