SDK : GLator transform 3D issue

Question

Hi everyone,  Maybe someone can help me:I have successfully run the GLator sample plugin, and modified it to display a different layer (user selects a layer in the UI, the plugin checkouts out the layer and passes it to OpenGL to display it). It works fine, however, I also want OpenGL to display the selected layer with its transform data (position, scale, rotation etc), even if it is 3D. Here is the code I've modified inside of the RenderGL() method. .....
// view matrix, mimic windows coordinates
vmath::Matrix4 ModelviewProjection = vmath::Matrix4::translation(vmath::Vector3(-1.0f, -1.0f, 0.0f)) * vmath::Matrix4::scale(vmath::Vector3(2.0 / float(widthL), 2.0 / float(heightL), 1.0f));
vmath::Matrix4 transformMatrix = A_Matrix4ToMatrix4(layerTransformMatrix4x4);
vmath::Matrix4 resultMatrix = ModelviewProjection * transformMatrix;

glBindTexture(GL_TEXTURE_2D, inputFrameTexture);
glUseProgram(renderContext->mProgramObjSu);

// program uniforms
GLint location = glGetUniformLocation(renderContext->mProgramObjSu, "ModelviewProjection");
glUniformMatrix4fv(location, 1, GL_FALSE, (GLfloat*)&resultMatrix);
..... Explanation:layerTransformMatrix4x4 is the transform matrix of the selected layer, that was retrieved using AEGP_GetLayerToWorldXform(). It contains all the transform data, even 3D. I then transform the matrix into a column matrix using A_Matrix4ToMatrix4(), and multiplied it with the ModelViewProjection matrix. The result is then passed to the vertex shader. The problem: it works fine for 2d translations, however 3d translations (with a different Z) results in a transparent layer. It does not draw anything! Am I missing something ? Thanks

Alex274279575dox · Accepted Answer

Ok so after some documentation, I figured out that OpenGL only draws the shapes that are contained in the camera frustum. So any shape whose coordinates are outside of the (-1,-1) clip limits is not drawn (that's why the first modelViewProjection matrix posted in this thread was wrong).

The modelViewProjection matrix provided in the GLator sample plugin is made like this :

2/width 0 0 -1

0 2/height 0 -1

0 0 1 0

0 0 0 1

So no information about the camera frustrum, or the Z position of the camera.

I tried to modify this matrix using this formula (found on internet) to include the far clipping plane, and the near clipping plane:

2/width 0 0 -1

0 2/height 0 -1

0 0 -1 / (far - near) -(far + near) / (far - near)

0 0 0 1

but... nothing, the render is still empty. Does anyone have an idea, or an example of code that works ?

Thanks a lot

Ok so I've managed to get it work !

The problem was that I was not multiplying the view matrix and the projection matrix in the correct order.

It should be

modelViewProjectionMatrix = projectionMatrix * modelViewMatrix;

in this order !

shachar carmi · Answer

did you check the content of resultMatrix on the 3D layer case? is any of the diagonal scale matrix entries a zero?

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