OpenGL Computer Graphics 3 — Questions and Answers
Question 1: In GLSL, which built-in variable contains the interpolated texture coordinate passed from the vertex shader to the fragment shader?
- A user-defined 'varying' or 'in' variable (Correct answer)
- gl_FragCoord
- gl_TexCoord
- gl_Position
Correct answer: A user-defined 'varying' or 'in' variable
Texture coordinates are user-defined 'out' variables in the vertex shader and matching 'in' variables in the fragment shader, interpolated by the rasterizer.
Question 2: What OpenGL call uploads a 2D texture image to the GPU?
- glTexImage2D() (Correct answer)
- glBindTexture()
- glGenTextures()
- glActiveTexture()
Correct answer: glTexImage2D()
glTexImage2D() specifies the mipmap level, internal format, dimensions, and pixel data for a 2D texture.
Question 3: What is mipmapping in OpenGL texturing?
- A series of pre-computed, progressively smaller texture images for minification (Correct answer)
- A technique to increase texture resolution dynamically
- Layered textures for cube mapping
- A method of compressing texture data on the GPU
Correct answer: A series of pre-computed, progressively smaller texture images for minification
Mipmaps are pre-filtered downsampled versions of a texture used when the textured surface is far from the camera to avoid aliasing.
Question 4: Which matrix transforms 3D eye-space coordinates into clip coordinates in a classic OpenGL pipeline?
- Projection matrix (Correct answer)
- Model matrix
- View matrix
- Normal matrix
Correct answer: Projection matrix
The projection matrix (perspective or orthographic) maps eye-space coordinates to the clip volume, defining the viewing frustum.
Question 5: What does the GLSL function 'normalize()' return?
- A vector with the same direction but a magnitude of 1.0 (Correct answer)
- The component-wise absolute value of the input
- The dot product of a vector with itself
- A vector clamped between 0.0 and 1.0
Correct answer: A vector with the same direction but a magnitude of 1.0
normalize(v) divides the vector by its length, returning a unit vector used frequently in lighting calculations.
Question 6: In OpenGL's stencil test, what does 'GL_KEEP' do when specified as the stencil operation?
- Leaves the stencil buffer value unchanged (Correct answer)
- Sets the stencil buffer value to zero
- Inverts all bits of the stencil value
- Replaces the stencil value with the reference value
Correct answer: Leaves the stencil buffer value unchanged
GL_KEEP is the no-op stencil operation that preserves the existing stencil value when the corresponding test result occurs.
Question 7: What is the purpose of calling glGenerateMipmap() after uploading a texture?
- Automatically generates all mipmap levels from the base level image (Correct answer)
- Compresses the texture to save VRAM
- Enables anisotropic filtering for the texture
- Binds the texture to all available texture units
Correct answer: Automatically generates all mipmap levels from the base level image
glGenerateMipmap() instructs the GPU to compute the full mipmap chain from the base texture image already uploaded.
OpenGL Computer Graphics 3
In GLSL, which built-in variable contains the interpolated texture coordinate passed from the vertex shader to the fragment shader?