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POImplementing a LookAt function in the Vertex Shader with OpenGL
 

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  1. POImplementing a LookAt function in the Vertex Shader with OpenGL
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    <p>For purposes beyond my control, I need to calculate a ModelView Matrix in my vertex shader. I understand this is a bad idea but I don't have a choice right now. Here is the code in my vertex shader. Based on <a href="https://stackoverflow.com/a/6802424">https://stackoverflow.com/a/6802424</a></p> <pre><code>mat4 lookAt(vec3 eye, vec3 center, vec3 up) { vec3 zaxis = normalize(center - eye); vec3 xaxis = normalize(cross(up, zaxis)); vec3 yaxis = cross(zaxis, xaxis); mat4 matrix; //Column Major matrix[0][0] = xaxis.x; matrix[1][0] = yaxis.x; matrix[2][0] = zaxis.x; matrix[3][0] = 0; matrix[0][1] = xaxis.y; matrix[1][1] = yaxis.y; matrix[2][1] = zaxis.y; matrix[3][1] = 0; matrix[0][2] = xaxis.z; matrix[1][2] = yaxis.z; matrix[2][2] = zaxis.z; matrix[3][2] = 0; matrix[0][3] = -dot(xaxis, eye); matrix[1][3] = -dot(yaxis, eye); matrix[2][3] = -dot(zaxis, eye); matrix[3][3] = 1; return matrix; } void main( void ) { vec3 cam = vec3(0, 0, 3); mat4 test = lookAt(cam, vec3(0,0,0), vec3(0, 1, 0)); gl_Position = gl_ProjectionMatrix * test * gl_Vertex; //gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex; } </code></pre> <p>However, when I use this in place of my ModelView Matrix, It doesn't work correctly. But I have no idea what is wrong. Can anyone point me in the right direction?</p> <p>Here are some pictures, although not terribly helpful.</p> <p>Using the programs ModelViewMatrix</p> <p><img src="https://i.imgur.com/a3fi26k.png" width="400" alt="Using the programs ModelViewMatrix"></p> <p>Using the Vertex Shader lookAt function</p> <p><img src="https://i.imgur.com/09oolMP.png" width="400" alt="Using the Vertex Shader lookAt function"></p>
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    1. PTQuestion
    1. USCommunity
    1. USJustin Egli
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      1. POImplementing a LookAt function in the Vertex Shader with OpenGL
      1. USluser droog
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    1. COHave you tried to transpose the matrix?
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      1. POImplementing a LookAt function in the Vertex Shader with OpenGL
      1. USNico Schertler
    2. COI've tried both before and after the dot(axis, eye) block.
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      1. POImplementing a LookAt function in the Vertex Shader with OpenGL
      1. USJustin Egli
    3. COHow can you transpose a matrix that has not been completely calculated? I mean swapping rows and columns.
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      1. POImplementing a LookAt function in the Vertex Shader with OpenGL
      1. USNico Schertler
 

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