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Unprojecting screen coordinates invalid result


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#1 Plerion   Members   -  Reputation: 367

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Posted 03 November 2012 - 07:04 PM

Hello everyone

On my tablet i render my scene to a depth buffer and read a pixel from it to determine my current position.

- I visualized the depth buffer -> all is fine, vertex shader:
[source lang="cpp"]varying float camDistance;void main() { vec4 tmpPos = vec4(vPosition0.xyz, 1.0); vec4 posCamSpace = matProj * matView * tmpPos; camDistance = (posCamSpace.z - 0.1) / (800.0 - 0.1); gl_Position = posCamSpace;}[/source]

i hardcoded the values just to be sure!

- I visualized the depth read from the buffer -> It is correct for the nearest points and for the points far away, thats the code i use:
[source lang="java"] ibuff.position(0); GLES20.glReadPixels((int)touchPos.x, (int)touchPos.y, 1, 1, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, ibuff); ibuff.position(0); int color = ibuff.getInt() & 0x000000FF; float depth = color / 256.0f;[/source]

- When i check my coordinates i see that it uses nearly the position of the camera for all 3 components and when i move my finger shifts the coorect coordinates but like 0.001 per pixel like so it seems that it unprojects the point no matter what depth i enter to the near plane.

- If I use depth 1 every time unprojection is done nicely and works like a charm if i move my finger, all coordinates are correct and change correct.

I used gluUnProject to unproject my values as well as my own implementation. With gluUnProject:
[source lang="java"] GLU.gluUnProject(touchPos.x, touchPos.y, depth, getActiveCamera().getMatView().getFloats(), 0, PerspectiveMatrix.getFloats(), 0, viewport, 0, coords, 0);[/source]

touchPos.y of course is transformed with the viewport (touchPos.y = viewport[3] - touchPos.y).

Thats my own implementation:
[source lang="java"] public static Vector3 unproject(Vector3 v, Matrix invView, Matrix invProj, int[] viewport) { Matrix matCombo = Matrix.multiply(invView, invProj); float vx = viewport[0]; float vy = viewport[1]; float vw = viewport[2]; float vh = viewport[3]; float[] rhsVec = { ((2 * (v.x - vx)) / vw) - 1, ((2 * (v.y - vy)) / vh) - 1, 2 * v.z - 1, 1 }; float[] result = new float[4]; android.opengl.Matrix.multiplyMV(result, 0, matCombo.getFloats(), 0, rhsVec, 0); float d = 1 / result[3]; return new Vector3(result[0] * d, result[1] * d, result[2] * d); }[/source]

What did i forget? I used gluUnProject on my Desktop with glReadPixels (but GL_DEPTH_COMPONENT which is not available on OpenGL ES) and it worked there!

Thank you for any help
Plerion

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#2 NumberXaero   Prime Members   -  Reputation: 1456

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Posted 03 November 2012 - 08:47 PM

The glu version is giving incorrect results also? Can you provide some numbers to give an idea of how incorrect it is?

Edited by NumberXaero, 03 November 2012 - 08:49 PM.


#3 Plerion   Members   -  Reputation: 367

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Posted 04 November 2012 - 05:22 AM

Sure, i made some screenshots from my tablet. Im sorry the font seems to be screwed up a bit, i hope its still readable, as i directly wrote into the screenshots! The big arrow always points to the location where my finger pressed. All the results come from the version with gluUnProject.

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#4 NumberXaero   Prime Members   -  Reputation: 1456

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Posted 04 November 2012 - 03:06 PM

Are these calls to unproject taking the model (world) matrix of that object into account? The original gluunproject call takes the modelView and projection matrix. I cant tell if the view matrix you pass includes the model matrix of the object being rendered.

#5 Plerion   Members   -  Reputation: 367

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Posted 04 November 2012 - 03:53 PM

Hey

The calls to the drawing for depth and visual are like that:
[source lang="java"] prog.setMatrix("matProj", Game.Instance.getGraphicsDevice().getProjMatrix()); prog.setMatrix("matView", Game.Instance.getGraphicsDevice().getActiveCamera().getMatView());[/source]

where getProjMatrix() returns the perspective matrix (PerspectiveMatrix) i pass to gluUnProject, getActiveCamera().getMatView() is what i use for gluUnProject too. So i use the absolut same matrices (there is no model matrix, they already have their absolute coordinates in the world).

#6 Plerion   Members   -  Reputation: 367

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Posted 05 November 2012 - 09:28 AM

This problem is starting to driving me mad... I now even put those goddamn matrices hardcoded for the shader and the gluUnProject, still gluUnProjects gives me complete garbage as result. The view-matrix seems to be correctly interpreted but the perspective matrix seems to be treated wrong. After closer inspection i realized that also for depth = 1 the results are rubbish. My cameras left to right axis is parallel to the y-axis, when i go with a constant depth of 1 from left to right it gives me a difference of 200 units, after calculating a bit that leads to a horizontal field of view of 15° which is clearly not the case. I do it the following way now:
[source lang="java"] GLU.gluUnProject(touchPos.x, y, depth, Matrix.LookAt(getActiveCamera().getPosition(), getActiveCamera().getFront(), getActiveCamera().getUp()).getFloats(), 0, Matrix.Perspective(45.0f, mWidth, mHeight, 1, 800.0f).getFloats(), 0, viewport, 0, coords, 0);[/source]

With the following functions:
[source lang="java"] public static Matrix Perspective(float fov, int width, int height, float zNear, float zFar) { Matrix ret = new Matrix(); android.opengl.Matrix.perspectiveM(ret.mMatrixFloats, 0, fov, ((float)width / height), zNear, zFar); return ret; } public static Matrix LookAt(Vector3 eye, Vector3 target, Vector3 up) { Matrix ret = new Matrix(); android.opengl.Matrix.setLookAtM(ret.mMatrixFloats, 0, eye.x, eye.y, eye.z, target.x, target.y, target.z, up.x, up.y, up.z); return ret; }[/source]

#7 Plerion   Members   -  Reputation: 367

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Posted 06 November 2012 - 03:00 AM

To conclude this topic:
I havent been able to actually solve the problem but i circumvented it. I do now all calculations by hand and the results are as i expected: Perfectly right!
[source lang="java"]public class Unproject { public void setPerspective(float fovy, float width, float height, float zNear, float zFar) { this.zNear = zNear; this.zFar = zFar; this.fovy = fovy; fovh = (width / height) * fovy; } public void setLookAt(Vector3 eye, Vector3 forward, Vector3 up, Vector3 right) { camEye = eye; camForward = forward; camUp = up; camRight = right; camRight.normalize(); camUp.normalize(); camForward.normalize(); } public void setViewport(int[] viewport) { this.viewport = viewport; } public Vector3 process(Vector3 screen) { float vx = viewport[0]; float vy = viewport[1]; float vw = viewport[2]; float vh = viewport[3]; screen.x = ((2 * (screen.x - vx)) / vw) - 1; screen.y = ((2 * (screen.y - vy)) / vh) - 1; float z = screen.z; float depth = zNear + (zFar - zNear) * Math.abs(z); float factor = 1; if(z < 0) { factor = -1; depth *= -1; } float lenh = (float)Math.tan(fovh * Math.PI / 360.0f) * depth; float lenv = (float)Math.tan(fovy * Math.PI / 360.0f) * depth; Vector3 target = Vector3.add(camEye, Vector3.mul(camForward, depth * factor)); target = Vector3.add(target, Vector3.mul(camRight, screen.x * lenh)); target = Vector3.add(target, Vector3.mul(camUp, lenv * screen.y)); return target; } private float zNear, zFar; private float fovy, fovh; private Vector3 camEye, camForward, camUp, camRight; private int[] viewport;}[/source]




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