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# Guido Granobles

Member Since 12 Jul 2011
Offline Last Active Nov 23 2012 06:07 PM

### How Render scene with 2 nested frames

08 November 2012 - 09:22 PM

Hi guys, I have been trying for long time figure out this:
I load a model from a directx file (I am using opnegl and Java) the model have a hierarchical system of nested reference frames (there are not bones). There is just 2 frames, one of them is called x3ds_Torso and it has a child frame called x3ds_Arm_01. Each one of them has a mesh. The thing is that I can't draw the arm connected to the body. Sometimes the body is in the center of the screen and the arm is at the top. Sometimes they are both in the center. I know that I have to multiply the matrix transformation of every frame by its parent frame starting from the top to the bottom and then I have to multiply every vertex of a mesh by its final transformation matrix. So I have this:

[source lang="java"]public void calculeFinalMatrixPosition(Bone boneParent, Bone bone) { System.out.println("-->" + bone.name); if (boneParent != null) { bone.matrixCombined = bone.matrixTransform .multiply(boneParent.matrixCombined); } else { bone.matrixCombined = bone.matrixTransform; } bone.matrixFinal = bone.matrixCombined; for (Bone childBone : bone.boneChilds) { calculeFinalMatrixPosition(bone, childBone); } }[/source]

Then multiply every vertex on the mesh:

[source lang="java"]public void transformVertex(Bone bone) { for (Iterator<Mesh> iterator = meshes.iterator(); iterator.hasNext();) { Mesh mesh = iterator.next(); if (mesh.boneName.equals(bone.name)) { float[] vertex = new float[4]; double[] newVertex = new double[3]; if (mesh.skinnedVertexBuffer == null) { mesh.skinnedVertexBuffer = new FloatDataBuffer( mesh.numVertices, 3); } mesh.vertexBuffer.buffer.rewind(); while (mesh.vertexBuffer.buffer.hasRemaining()) { vertex[0] = mesh.vertexBuffer.buffer.get(); vertex[1] = mesh.vertexBuffer.buffer.get(); vertex[2] = mesh.vertexBuffer.buffer.get(); vertex[3] = 1; newVertex = bone.matrixFinal.transpose().multiply(vertex); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[0])); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[1])); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[2])); } mesh.vertexBuffer = new FloatDataBuffer( mesh.numVertices, 3); mesh.skinnedVertexBuffer.buffer.rewind(); mesh.vertexBuffer.buffer.put(mesh.skinnedVertexBuffer.buffer); } } for (Bone childBone : bone.boneChilds) { transformVertex(childBone); } }[/source]

I know this is not the most efficient code but by now I just want to understand exactly how a hierarchical model is organized and how can I draw it on the screen.