Sample questions
Gfx Shadows Depth PrecisionDifficulty 1
In classic shadow mapping, what is rendered from the light's point of view before the main camera pass?
- aA depth-only image of the scene✓
- bA fully shaded color image of the scene
- cA screen-space normal buffer
- dA stencil mask of lit pixels
Explanation:Shadow mapping renders the scene from the light's viewpoint and keeps only depth values. The camera pass later compares each fragment's distance to the light against this stored depth to decide occlusion.
Gfx Shadows Depth PrecisionDifficulty 1
Which projection is typically used to render the shadow map for a directional light such as sunlight?
- aPerspective projection
- bCube map projection
- cOrthographic projection✓
- dDual-paraboloid projection
Explanation:A directional light has parallel rays and no single origin point, so its shadow map is rendered with an orthographic projection; spot lights use perspective, and point lights commonly use a cube map or dual-paraboloid projection.
Gfx Shadows Depth PrecisionDifficulty 2
A point light radiates in every direction. Which approach commonly covers the full sphere of directions for its shadow map?
- aA single orthographic shadow map
- bA shadow map aligned to the camera frustum
- cA cascaded set of orthographic maps
- dA cube map with one depth pass per face✓
Explanation:A point light has no single forward direction, so one perspective map cannot cover it. A common solution renders depth into six faces of a cube map, one per axis direction; dual-paraboloid mapping is an alternative.
Gfx Shadows Depth PrecisionDifficulty 2
A lit flat floor shows dark diagonal stripes that flicker even though nothing occludes it. What artifact is this?
- aPeter-panning
- bShadow acne✓
- cLight leaking
- dTexture bleeding
Explanation:This is shadow acne: incorrect self-shadowing stripes on an otherwise lit surface, caused by the shadow map's quantized depth wrongly comparing a surface as farther from the light than itself.
Gfx Shadows Depth PrecisionDifficulty 2
QA reports a visible gap between a character's feet and its own shadow on the ground. What is this artifact called?
- aShadow acne
- bCascade seam
- cPeter-panning✓
- dLight leaking
Explanation:Peter-panning is the visible detachment of a shadow from the object casting it, most often caused by a depth bias large enough to push the compared shadow surface too far away.
Gfx Shadows Depth PrecisionDifficulty 2
Light visibly appears in a corner where two shadowed walls should fully block it, near a thin occluding edge. What is this called?
- aLight leaking✓
- bShadow acne
- cZ-fighting
- dPeter-panning
Explanation:Light leaking is light incorrectly reaching an area that should be fully occluded. It commonly shows up near thin occluders where shadow-map resolution or bias is not enough to represent the edge correctly.