Android GLES2.0：基本矩阵问题

Question

I'm beginning in OpenGL ES on Android (Java); I'm following this tutorial : http://developer.android.com/training/graphics/opengl/projection.html

Things basically go well, except that I have some trouble with matrix-multiplication that I didn't have on desktop OpenGL (where I used GLM instead of java/android framework) My projection+view matrix does'nt work correctly when I do projection * view * vec4(..coords..) The only way for my geometry to be shown is to multiply by right : vec4(...) * MVP, where MVP is Projection*View. It shouldn't work (as far as I'm concerned) but... it does. At least a little bit. I get massive clipping problems by using this way, but it's still better than nothing :D

My problem is kinda similar to this (and same tutorial, but it looks like it got updated) : Android OpenGL weirdness with the setLookAtM method

But it looks like I have the opposite problem now. And I've tried every combination I've imagined to solve this (transpose MVP in GLSL, multiply view by projection and not the other way around, etc.)

Here's my code

 //GLSL :
 gl_Position =  vec4(vPosition, 1.0) * MVP;

Where MVP is mMVPMatrix, which is defined as ...

 Matrix.setLookAtM(mCameraMatrix, 0, 8, 8, -8, 0f, 0f, 0f, 0.0f, 1.0f, 0.0f);
 Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mCameraMatrix, 0);

And projection is

float ratio = (float) width / height;

android.opengl.Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 3, 7);

Any idea ?

Answer 1

解决的问题：我只需要在计算MVP矩阵之前将其设置为Identity，然后每一帧