Glossary

The words, without the hand-waving.

55 terms this site actually uses, defined in plain language. 43 of them link to a lab that demonstrates the idea, because the fastest definition of “perspective divide” is a slider that performs one.

Aliasing See it · Textures & Sampling: What happens when a signal is sampled too sparsely to represent it — jagged edges, and the crawling shimmer on a detailed texture seen at a distance. Mipmaps and anti-aliasing are two different answers to it.; See alsoMipmap Filtering Rasterisation
Attribute: Per-vertex input to a vertex shader — position, normal, colour, texture coordinate. Each vertex gets its own value, read from a buffer you describe the layout of.; See alsoUniform Varying Vertex
Backface culling: Discarding triangles that face away from the camera before they are rasterised, decided by winding order. Roughly halves the work on a closed shape, and makes a model with inconsistent winding look full of holes.; See alsoWinding order Rasterisation
Basis vectors See it · The Model Matrix: The three vectors a transform sends the x, y and z axes to. They are literally the first three columns of the matrix, which is why colouring those columns and colouring the axes on screen shows the same thing twice.; See alsoModel matrix Homogeneous coordinates Vertex
Batching See it · Draw Calls & Instancing: Merging things that would have been separate draw calls into one — same material, same buffer, submitted together. Instancing is the case where the merged objects are identical; batching more generally is why engines fight so hard to keep materials uniform.; See alsoDraw call Instancing
Clip space See it · Coordinate Spaces: Where vertices land after the projection matrix and before the perspective divide. Coordinates are homogeneous — a point survives clipping when each of x, y and z lies within ±w. Still a pyramid at this point, not a cube.; See alsoNDC Perspective divide Homogeneous coordinates
Composition order See it · The Model Matrix: The order matrices are multiplied in, which is not commutative and reads right to left: in T · R · S the scale reaches the vertex first. Swap two and the object goes somewhere else entirely.; See alsoModel matrix Basis vectors
Compute shader See it · Compute & Particles: A shader that is not part of the drawing pipeline. It has no vertices and no fragments — just a grid of invocations reading and writing buffers. WebGL has no such stage at all.; See alsoWorkgroup Storage buffer Shader
CPU-bound See it · Draw Calls & Instancing: When the frame time is set by how fast the CPU can prepare and submit work rather than by how fast the GPU can execute it. The tell is that reducing triangles changes nothing while reducing draw calls changes everything.; See alsoDraw call Instancing
Depth buffer: A per-pixel record of how far away the nearest thing drawn so far is, so a fragment behind it can be discarded. Also called the z-buffer. It is why you can draw geometry in any order and still get correct occlusion.; See alsoFragment NDC
Draw call See it · Draw Calls & Instancing: One instruction from the CPU telling the GPU to render something. Each one costs CPU time to validate and submit whether it draws two triangles or two million, which is why a scene can be limited by how many times you asked rather than by how much you asked for.; See alsoInstancing CPU-bound Batching
Filtering See it · Textures & Sampling: How the sampler combines texels. Nearest takes one; bilinear blends four; trilinear blends bilinear results from two mip levels. Minification and magnification are set separately because they are different problems.; See alsoMipmap Texel Aliasing
Flat shading See it · Light & Normals: One normal per triangle, so each face is a single constant colour. You are seeing the mesh rather than the surface it approximates, which is sometimes exactly what you want.; See alsoNormal Gouraud shading
Fragment: A candidate pixel produced by rasterising a triangle — it has a position, interpolated attributes and a depth, but has not yet won its place in the framebuffer. A fragment shader runs once per fragment.; See alsoRasterisation Shader Depth buffer
Frustum See it · Projection & the Frustum: The truncated pyramid of space a perspective camera can see, bounded by the near and far planes. Not a thing you build: it is the canonical clip cube pulled back through the inverse of the projection matrix.; See alsoNear and far planes Projection matrix Clip space
Gamma See it · Colour & Gamma: The exponent relating an encoded colour value to the light it stands for — about 2.2 for sRGB. Raising a value to that power decodes it to light; the reciprocal encodes it back.; See alsosRGB Linear colour
Gamma correction See it · Colour & Gamma: Decoding colours to linear before lighting them and encoding the result back for display. Skipping it does not throw an error or look obviously broken — it darkens midtones and hardens the terminator, which reads as a lighting choice, which is why it ships.; See alsoGamma Linear colour sRGB
GLSL: The OpenGL Shading Language, used by WebGL. C-like, with first-class vector and matrix types. Its WebGPU counterpart is WGSL.; See alsoWGSL Shader
Gouraud shading See it · Light & Normals: Lighting computed once per vertex, with the resulting colour interpolated across the triangle. Cheap, and it loses any highlight smaller than a triangle — which is most of them.; See alsoPhong shading Flat shading Varying
Homogeneous coordinates See it · The Model Matrix: Adding a fourth component, w, to a 3D point so that translation becomes a matrix multiply like everything else. Points carry w = 1; directions carry w = 0, which is why translating a direction correctly does nothing.; See alsoPerspective divide Clip space
Instance index See it · Draw Calls & Instancing: The counter a vertex shader reads to know which copy it is drawing — `gl_InstanceID` in GLSL, `@builtin(instance_index)` in WGSL. It is what turns one set of vertices into a field of objects, by indexing per-instance data with it.; See alsoInstancing Storage buffer Vertex
Instancing See it · Draw Calls & Instancing: Drawing the same geometry many times in one call, with per-instance data supplying what differs. The saving is not in triangles but in draw calls, which is usually where the CPU time actually goes.; See alsoDraw call Instance index Batching
Lambert See it · Light & Normals: The diffuse term: brightness proportional to how squarely a surface faces the light, and nothing else. It is the cosine of the angle between the normal and the light direction, clamped at zero so surfaces turned away are unlit rather than negatively lit.; See alsoNormal Specular highlight Linear colour
Linear colour See it · Colour & Gamma: Colour whose numbers are proportional to actual light, so doubling the number doubles the brightness. The only space in which adding two lights together, or multiplying by a Lambert term, means what the arithmetic says it means.; See alsosRGB Gamma correction Lambert
Mipmap See it · Textures & Sampling: The same texture pre-shrunk by half repeatedly, so there is always a level where one texel is about one pixel. Costs a third more memory and removes an entire class of artefact.; See alsoAliasing Filtering Texel
Model matrix See it · The Model Matrix: Places an object in the world: its translation, rotation and scale combined. The only matrix in the chain you usually author by hand.; See alsoView matrix Projection matrix Model space
Model space See it · Coordinate Spaces: The coordinate system a mesh was authored in, centred on its own origin. Nothing has happened to it yet.; See alsoWorld space Model matrix
NDC See it · Coordinate Spaces: Normalised device coordinates: what you get after dividing clip space by w. A cube from −1 to 1 on every axis. Everything outside it is discarded, and everything inside it is about to become pixels.; See alsoClip space Perspective divide Viewport
Near and far planes See it · Projection & the Frustum: The front and back of the frustum. They are a hard clip, not a fade — geometry crossing them is cut. Putting near too close crushes depth precision, which is where z-fighting comes from.; See alsoFrustum Depth buffer
Normal See it · Light & Normals: A unit vector perpendicular to a surface at a point, describing which way it faces. Lighting is almost entirely a question of the angle between the normal and the light.; See alsoNormal matrix Flat shading
Normal matrix See it · Light & Normals: The inverse-transpose of the model matrix, used to transform normals. A normal describes an orientation, not a position, so scaling one axis must tilt it rather than squash it. Under uniform scale it reduces to the model matrix, which is why getting this wrong stays invisible for so long.; See alsoNormal Model matrix
Orthographic projection See it · Projection & the Frustum: A projection whose view volume is a box rather than a pyramid. w stays 1, so no perspective divide happens and distance never changes size. Right for CAD and isometric games, wrong for anything meant to look photographed.; See alsoPerspective projection Projection matrix
Perspective divide See it · Coordinate Spaces: Dividing x, y and z by w, performed by the GPU between the vertex shader and rasterisation. This single division is what makes distant things small — the projection matrix only arranges for w to carry the depth.; See alsoClip space NDC Homogeneous coordinates
Perspective projection See it · Projection & the Frustum: A projection whose view volume is a frustum. Its defining feature is a −1 in the bottom row, which copies −z into w so the divide can shrink things with distance.; See alsoOrthographic projection Frustum Perspective divide
Phong shading See it · Light & Normals: Interpolating the normal across a triangle and computing lighting per fragment. More expensive than Gouraud and it puts highlights where they belong. Not to be confused with the Phong reflection model, which is the equation rather than where you evaluate it.; See alsoGouraud shading Specular highlight Fragment
Projection matrix See it · Projection & the Frustum: Turns view space into clip space, deciding the shape of the visible volume — field of view, aspect ratio, near and far. It does not itself divide anything.; See alsoPerspective projection Clip space View matrix
Rasterisation: Working out which pixels a triangle covers, and interpolating the vertex outputs across them. The step between geometry and fragments, and the reason GPUs are shaped the way they are.; See alsoFragment Varying
Shader: A small program that runs on the GPU, once per vertex or once per fragment, in parallel across thousands of them. Vertex shaders decide where things are; fragment shaders decide what colour they are.; See alsoGLSL WGSL Fragment
Specular highlight See it · Light & Normals: The bright spot where a surface reflects the light source towards the eye. Its tightness is controlled by a shininess exponent; its presence is most of what makes a material look wet, polished or metallic.; See alsoPhong shading Normal
sRGB See it · Colour & Gamma: The colour space almost every image, screen and colour picker uses. It is deliberately non-linear — more of its range is spent on dark tones, because eyes are more sensitive there — which means the numbers in it are not proportional to light.; See alsoLinear colour Gamma Gamma correction
Storage buffer See it · Compute & Particles: GPU memory a shader can write to as well as read, unlike a uniform. It is what lets simulation state live on the GPU across frames instead of being shipped back and forth.; See alsoCompute shader Uniform Workgroup
Texel See it · Textures & Sampling: One pixel of a texture, as opposed to one pixel of the screen. The whole business of texture filtering is deciding what to do when those two do not line up.; See alsoTexture Mipmap Filtering
Texture See it · Textures & Sampling: An image sampled by a shader. Usually colour, but just as often a normal map, a height field, a mask, or an arbitrary lookup table — to the GPU it is only structured memory you can interpolate.; See alsoTexel UV coordinates Filtering
Uniform: A value that is the same for every vertex and fragment in a draw call — a matrix, a light direction, the current time. Set from JavaScript, read-only inside the shader.; See alsoAttribute Shader
UV coordinates See it · Textures & Sampling: The 2D coordinates that say where on a texture a vertex samples from, conventionally 0 to 1 across the image. Called u and v so as not to collide with x, y and z.; See alsoTexture Wrap mode Attribute
Varying: A value passed from the vertex shader to the fragment shader, interpolated across the triangle on the way. The mechanism behind Gouraud shading, texture coordinates and smooth colour.; See alsoAttribute Rasterisation Gouraud shading
Vertex: A point of geometry with attributes attached. Not quite the same as a corner: two faces meeting at one corner need two vertices if their normals differ.; See alsoAttribute Flat shading
View matrix See it · Coordinate Spaces: Moves the world so the camera sits at the origin looking down −Z. There is no camera object on a GPU; there is only this inverse.; See alsoView space Model matrix Projection matrix
View space See it · Coordinate Spaces: Coordinates relative to the camera, after the view matrix. The camera is at the origin here, by construction.; See alsoView matrix World space
Viewport See it · Coordinate Spaces: The rectangle of pixels being drawn into, and the final transform from NDC to pixel coordinates. Note that y flips: NDC counts up, pixel rows count down.; See alsoNDC Rasterisation
WGSL: The WebGPU Shading Language. Rust-flavoured rather than C-flavoured, strongly typed, with explicit binding annotations. Same job as GLSL, different spelling.; See alsoGLSL Shader
Winding order: Whether a triangle’s vertices are listed clockwise or counter-clockwise on screen, which is how the GPU decides which side is the front. Get it inconsistent and backface culling eats half your model.; See alsoBackface culling Vertex
Workgroup See it · Compute & Particles: The unit a compute dispatch is divided into — a small block of invocations that run together and can share memory. You choose the size; 64 is a common default because it maps well to the hardware.; See alsoCompute shader Storage buffer
World space See it · Coordinate Spaces: The shared coordinate system the scene lives in, after each object’s model matrix has placed it. The only space where "next to" means what you think it means.; See alsoModel space View space Model matrix
Wrap mode See it · Textures & Sampling: What the sampler does with a UV outside 0…1. Repeat tiles it, clamp smears the edge texel outward, mirror flips alternate tiles so the seams line up.; See alsoUV coordinates Texture