Here's the vertex shader:
uniform mat4 projection;
uniform mat4 view;
uniform mat4 model;
void main(void)
{
gl_Position = projection * view * model * gl_Vertex;
gl_TexCoord[0] = gl_MultiTexCoord0;
}
My understanding is that using various transformations, the model space eventually turns into a clip space, which is a field connected by each element on each axis, facing directly to the viewport, i.e. something in (-1, 1, 0) is in the upper left corner of the viewport. When I remove all matrix transformations from the shader,
gl_Position = gl_Vertex;
and pass as a model a simple quad
public Vector3[] verts = new Vector3[] {
new Vector3(-1f, -1f, 0),
new Vector3(1f, -1f, 0),
new Vector3(1f, 1f, 0),
new Vector3(-1f, 1f, 0),
};
public Vector2[] coords = new Vector2[] {
new Vector2(0, 1f),
new Vector2(1f, 1f),
new Vector2(1f, 0f),
new Vector2(0f, 0f),
};
public uint[] indices = new uint[] {
0,1,2,
0,2,3,
};
I get the expected full screen image. When I apply transformations, the image appears as expected, a small square in the center of the screen. The problem arises when I try to calculate the position of the model vertex in the clip coordinates on the CPU:
public Vector4 testMult(Vector4 v, Matrix4 m)
{
return new Vector4(
m.M11 * v.X + m.M12 * v.Y + m.M13 * v.Z + m.M14 * v.W,
m.M21 * v.X + m.M22 * v.Y + m.M23 * v.Z + m.M24 * v.W,
m.M31 * v.X + m.M32 * v.Y + m.M33 * v.Z + m.M34 * v.W,
m.M41 * v.X + m.M42 * v.Y + m.M43 * v.Z + m.M44 * v.W);
}
Matrix4 test = (GlobalDrawer.projectionMatrix * GlobalDrawer.viewMatrix) * modelMatrix;
Vector4 testv = (new Vector4(1f, 1f, 0, 1));
Console.WriteLine("Test Input: " + testv);
Console.WriteLine("Test Output: " + Vector4.Transform(testv, test));
Vector4 testv2 = testMult(testv, test);
Console.WriteLine("Test Output: " + testv2);
Console.WriteLine("Test Output division: " + testv2 / testv2.W);
(The resulting matrices are identical to those transmitted to the shader)
, W 0:
Test Input: (1, 1, 0, 1)
Test Output: (0.9053301, 1.207107, -2.031746, 0)
Test Output: (0.9053301, 1.207107, -1, 0)
Test Output division: (Infinity, Infinity, -Infinity, NaN)
:
projectionMatrix = Matrix4.CreatePerspectiveFieldOfView((float)Math.PI / 4, window.Width / (float)window.Height, 1.0f, 64.0f);
projectionMatrix =
(1.81066, 0, 0, 0)
(0, 2.414213, 0, 0)
(0, 0, -1.031746, -1)
(0, 0, -2.031746, 0)
viewMatrix = Matrix4.LookAt(new Vector3(0,0,4), -Vector3.UnitZ, Vector3.UnitY);
viewMatrix =
(1, 0, 0, 0)
(0, 1, 0, 0)
(0, 0, 1, 0)
(0, 0, -4, 1)
modelMatrix =
(0.5, 0 , 0 , 0)
(0 , 0.5, 0 , 0)
(0 , 0 , 1 , 0)
(0 , 0 , 0 , 1)
, , ; ?