OpenGL Computer Graphics 2

Question 1

Which OpenGL function is used to specify the color used when the color buffer is cleared?

Accepted Answer

glClearColor()

Answer

glClearColor() sets the RGBA values used when glClear(GL_COLOR_BUFFER_BIT) is called.

Question 2

In OpenGL's clip coordinate system, what is the valid range for the w-component after perspective division?

Accepted Answer

It must be positive

Answer

After perspective division, the w component must be positive for a vertex to be on the visible side of the projection plane.

Question 3

What does the OpenGL function glScissor() do?

Accepted Answer

Defines a rectangular region outside which all rendering is discarded

Answer

glScissor() defines a rectangular scissor box; fragments outside this box are discarded before the color buffer is updated.

Question 4

Which blending equation makes a fragment fully transparent when its alpha value is 0?

Accepted Answer

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)

Answer

GL_SRC_ALPHA / GL_ONE_MINUS_SRC_ALPHA is the standard alpha blending equation that makes alpha=0 fragments fully transparent.

Question 5

In OpenGL, what is a Framebuffer Object (FBO) primarily used for?

Accepted Answer

Off-screen rendering to textures or renderbuffers

Answer

FBOs allow rendering to non-default framebuffers, enabling off-screen rendering, render-to-texture, and post-processing effects.

OpenGL Practice Test