Correct Vertex Shader Code? Opengl Es 2.0

Edit Code added, please see below Edit 2 - Screenshots from device included at bottom along with explanation Edit 3 - New code added I have 2 classes, a rendered and a custom 'quad

Solution 1:

It's really impossible to tell because we don't know what you are passing to these two variables.

OpenGL is column-major format, so if vPosition is in fact a vector, and uMVPMatrix is a matrix, then the first option is correct, if this is in your shader.

If this is not in your shader but in your program code, then there is not enough information.

If you are using the first option but getting unexpected results, you are likely not computing your matrix properly or not passing the correct vertices.

Solution 2:

Normally in the vertex shader you should multiple the positions by the MVP, that is

gl_Position = uMVPMatrix *vPosition;

When you change the order this should work...

Solution 3:

Thanks to all for the help.

I managed to track down the problem (For the most part). I will show what I did.

It was the following line:

Matrix.multiplyMM(mvpMatrix, 0, mvpMatrix, 0, mRotationMatrix, 0);

As you can see I was multiplying the matrices and storing them back into one that I was using in the multiplication.

So I created a new matrix called mvpMatrix2 and stored the results in that. Then passed that to my vertex shader.

//Multiply matrices
Matrix.multiplyMM(mvpMatrix2, 0, mvpMatrix, 0, mRotationMatrix, 0);

//get handle to shape's transformation matrix
mMVPMatrixHandle = GLES20.glGetUniformLocation(iProgId, "uMVPMatrix");

//Give to vertex shader variable
GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix2, 0);

After applying this, there is no distortion (And also, with regards to my other question here Using Matrix. Rotate in OpenGL ES 2.0 I am able to translate the centre of the quad). I say 'for the most part' because however, when I rotate it, it rotates backwards (so if I say rotate +45 degrees, (Clockwise), it actually rotates the quad by -45 degrees (Anit-clockwise).

But hopefully, this will help anyone who has a similar problem in the future.