teaching machines

CS 455 Lecture 5 – Vectors, Matrices, and Meshes

February 5, 2013 by Chris Johnson. Filed under cs455, lectures, spring 2013.

Before Class

Meshes

• Watch http://youtu.be/EWtMydWVozQ.
• Watch an introduction to modeling: http://cgcookie.com/blender/2010/08/31/blender-intro-to-modeling.

Vectors and Matrices

• Watch http://youtu.be/cMkKKDanIhw.
• Read http://www.gamedev.net/page/resources/_/technical/math-and-physics/vectors-and-matrices-a-primer-r1832, skipping the sections on determinants, inversion, and projection matrices for now.

In class

• Create a renderer that lets you scale and or translate a tweaked OBJ model with a matrix. (I’ve placed a few models in the W455 directory.) Alter your matrix based on events of your choosing. (Recognizing cursor key events needs to be added to glut_utilities.cpp. It’s simple to do; follow the PAGEUP example or ask if you need help.)
• The GPU can do matrix multiplication out of the box. Send your matrix as a uniform:

  uniform mat4 xform;
  in vec3 position;
  
  void main() {
    gl_Position = xform * vec4(position, 1.0);
  }

• On the CPU side of things, you need to store your matrix in memory somehow. Next lecture will cover making a handy matrix class. For now, just store matrix elements in a one-dimensional array in column-major order:

  scale as {sx, 0, 0, 0, 0, sy, 0, 0, 0, 0, sz, 0, 0, 0, 0, 1}
  translate as {1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, dx, dy, dz, 1}

• Send your matrix to the GPU uniform with something like:

  program->Bind();
  GLint location = program->GetUniformLocation("xform");
  glUniformMatrix4fv(location, 1, GL_FALSE, scaleOrTranslateMatrix);
  program->Unbind();

• Give yourself a pat on the back!

Haiku