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Sample Test 2
4-digit grading ID:
Name:
IMPORTANT: State any (reasonable) assumption you make to complete the answer. A yes or no answer without explanation is worth 0 points. You may use the book(s). Write answers cleanly on the space provided. Use the back of the previous page if more space is needed. Clear sketches are encouraged.
1 Techniques and Concepts
[6] Describe, in a sentence or two, or using a sketch, the relationship of each of the following pairs of terms.
(A) Painter’s algorithm and z-buffering.
(B) Clipping and the viewing frustum.
(C) Bump mapping and surface normals.
(D) Bresenham’s algorithm and Nurbs curves.
(E) Minkowski sum and morphing.
(F) Simplex and icosahedron.
2 glMap2 - Surfaces
Consider the following control points
GLfloat ctrlpoints[2][3][4] = { {{{0.0, 0.0,2.0,2.0}, {0.0, 0.5,0.5,1.0}, {0.0, 1.0,0.0,1.0}}, {{1.0, 0.0,0.0,1.0}, {1.0,0.5,0.5,1.0}, {0.5, 0.5,0.5,0.5}}}};
and the definition of the corresponding B´ezier map
glMap2f(GL_MAP2_VERTEX_4, 0, 1, A, B, 0, 1, C, 2, &ctrlpoints[0][0][0]);
Give appropriate values for A, B and C (with comment). Compute the value of the surface at u = v = 1/2 using de Casteljau’s algorithm.
4 Stencils and Map
[2+2] A stencil application is defined as follows
GLfloat ctrlpoints[333] = { -1,-1,0, 0,-1.5,0, 1,-1,0, -1.5,0,0 , 0,0, 0, 1.5,0,0, -1, 1,0, 0, 1.5,0, 1,1,0 };
In init
glClearStencil(0x0); glEnable(GL_STENCIL_TEST); glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 3, 0, 1, 9, 3, &ctrlpoints[0]); glEnable(GL_MAP2_VERTEX_3); glMapGrid2f(20, 0.0, 1.0, 20, 0.0, 1.0);
In reshape
glClear(GL_STENCIL_BUFFER_BIT); glStencilFunc (GL_ALWAYS, 0x1, 0x1); glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE); glEvalMesh2(GL_FILL, 0, 20, 0, 20);
In display
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glStencilFunc (GL_EQUAL, 0x1, 0x1); glColor3f(1.0,0.0,0.0); glBegin(GL_QUADS); glVertex2f (-0.5, -0.5); glVertex2f ( 0.5, -0.5); glVertex2f ( 0.5, 0.5); glVertex2f (-0.5, 0.5); glEnd(); glStencilFunc (GL_NOTEQUAL, 0x1 , 0x1); glColor3f(0.0,0.0,1.0); glBegin(GL_QUADS); glVertex2f (-1.5, -1.5); glVertex2f ( 1.5, -1.5); glVertex2f ( 1.5, 1.5); glVertex2f (-1.5, 1.5); glEnd();
What is visible on the screen after reshape and display have been called? De- scribe shapes, specify colors!
