Jump to content
  • Advertisement
Sign in to follow this  
prototypev

OpenGL Having problems with gluUnproject

This topic is 4577 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Greetings to everyone, I'm having some problems with gluUnproject. First off, I have a model of a building, in which I draw, then translate, rotate, and scale to fit my requirements. (for simplicity sake, we'll just take it that the yMin = 0 and yMax = 80, scale factor = 0.2) Now I'm trying to determine the actual co-ordinate when the user clicks on a specific region within the building by using gluUnproject, however the returned co-ordinates (I'm not too concerned with the x and z for the moment) don't seem to be correct at all. Just to give an illustration, when I click at the bottom of the building, the returned y value is 5.2079742665861311, when I click at the top of the building, the returned y value is 5.2433680417046098. This is clearly wrong :( I've read that this could be due to having a wrong projection or model matrix, but I'm kind of new to OpenGL, is there a way to verify this? Help would be greatly appreciated. BTW, here is my code snippet for the gluUnproject (it's exactly the same one found at http://nehe.gamedev.net/data/articles/article.asp?article=13: CVector3 GetOGLPos(int x, int y) { GLint viewport[4]; GLdouble modelview[16]; GLdouble projection[16]; GLfloat winX, winY, winZ; GLdouble posX, posY, posZ; glGetDoublev( GL_MODELVIEW_MATRIX, modelview ); glGetDoublev( GL_PROJECTION_MATRIX, projection ); glGetIntegerv( GL_VIEWPORT, viewport ); winX = (float)x; winY = (float)viewport[3] - (float)y; glReadPixels( x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ ); gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ); return CVector3(posX, posY, posZ); } [Edited by - prototypev on December 6, 2005 2:52:10 AM]

Share this post


Link to post
Share on other sites
Advertisement
it should work
to debug try printing out all the values onscreen
eg mouse x,y + zdepth (under cursor)
and print out the x,y,z result from the unproject command
move the mouse around and see whats happening

Share this post


Link to post
Share on other sites
Most likely your unprojected point is in world coordinates and you are expecting object relative coordinates. Rather than comparing the unprojected point to the vertices of the object compare it to the position of the object. Pretty much to get object relative coordinates you have to know which object it is so you can load the right modelview matrix. Depending upon what you are doing determining the right object may be all you need to do.

Share this post


Link to post
Share on other sites
Quote:
Original post by zedzeek
it should work
to debug try printing out all the values onscreen
eg mouse x,y + zdepth (under cursor)
and print out the x,y,z result from the unproject command
move the mouse around and see whats happening


As currently theres only one object in the scene, I only tested mousing on this object. The depth value always remains the same no matter where I click, that's one (seems wierd, as the different points I clicked should have different depth values I think). Secondly, the x and y variation is very very small, as what I highlighted above.

Share this post


Link to post
Share on other sites
Quote:
Original post by LilBudyWizer
Most likely your unprojected point is in world coordinates and you are expecting object relative coordinates. Rather than comparing the unprojected point to the vertices of the object compare it to the position of the object. Pretty much to get object relative coordinates you have to know which object it is so you can load the right modelview matrix. Depending upon what you are doing determining the right object may be all you need to do.


Please pardon my newbness but does that mean I should do my translation, rotation, scaling on the modelview matrix depending on which object is being chosen, BEFORE I attempt to do gluUnProject?

Share this post


Link to post
Share on other sites
No, you would just want to apply the inverse of the translation of the object then the inverse of its orientation/rotation on the value you get when you click on it. That would give you the coordinate in object space.

Share this post


Link to post
Share on other sites
Quote:
As currently theres only one object in the scene, I only tested mousing on this object. The depth value always remains the same no matter where I click, that's one (seems wierd, as the different points I clicked should have different depth values I think). Secondly, the x and y variation is very very small, as what I highlighted above

never assume it leads to problems
do what i said + print out the 6 values every frame preferably onscreen

Share this post


Link to post
Share on other sites
I'm getting confused :(

Ok here's what I did when I rendered the object:

glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glTranslatef(obj->x, obj->y, obj->z);
glRotatef(obj->orientation, 0, 1, 0);
glScalef(obj->scale, obj->scale, obj->scale);
glPopMatrix();

So, I modified the existing function containing gluUnProject to:

GLdouble MyFunc(int mousex, int mousey) {

GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);

GLdouble modelview[16], projection[16];
GLfloat winZ;
GLdouble posX, posY, posZ;

glGetDoublev(GL_PROJECTION_MATRIX, projection);

glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glScalef(1/obj->scale, 1/obj->scale, 1/obj->scale);
glRotatef(-obj->orientation, 0, 1, 0);
glTranslatef(-obj->x, -obj->y, -obj->z);

glGetDoublev(GL_MODELVIEW_MATRIX, modelview);

GLint winY = viewport[3] - mousey - 1;
glReadPixels(mousex, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ);

gluUnProject((double)mousex, (double)winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
glPopMatrix();

return posY;
}

The co-ordinates I get at the bottom and top of the object are still incorrect :(

Once again, please pardon my newbness.

Share this post


Link to post
Share on other sites
Quote:
Original post by prototypev
Quote:
Original post by LilBudyWizer
Most likely your unprojected point is in world coordinates and you are expecting object relative coordinates. Rather than comparing the unprojected point to the vertices of the object compare it to the position of the object. Pretty much to get object relative coordinates you have to know which object it is so you can load the right modelview matrix. Depending upon what you are doing determining the right object may be all you need to do.


Please pardon my newbness but does that mean I should do my translation, rotation, scaling on the modelview matrix depending on which object is being chosen, BEFORE I attempt to do gluUnProject?


Actually, I think the answer to this is yes. I was messing around with gluUnproject a while back, and I was getting wrong coordinate values returned. It turned out that I needed to be using the projection/modelview matrix that resulted from my call to gluLookAt (or in your case, the series of translates, rotates, and scales).

Share this post


Link to post
Share on other sites
No, you don't want to invert the modelview matrix. The stuff about inversion is an optimization and you aren't to that point yet. You just need to use the same modelview matrix you used to draw the object. Once you get multiple objects you won't know which modelview matrix is the correct one. So you do all of them. You use the modelview matrix used to draw an object and check the unprojected point against that object. Once you have that working then you can worry about using the inverse of the object to world transform to avoid repeating the screen to world transform. Optimization comes last. Once you are doing everything you have to do then you worry about doing it faster.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Similar Content

    • By plz717
      Hello, everyone! I hope my problem isn't too 'beginnerish'. I'm doing research on motion synthesis now, trying to implement the Deep Mimic paper (DeepMimic) by BINPENG XUE, in this paper, I need to first retarget character A's motion to another character B to make the reference motion clips for character B, since we don't have character B‘s reference motion. The most important thing is that in the paper, the author copied character A's joint's rotation with respective to joint's local coordinate system (not the parent) to character B. In my personal understanding, the joint's rotation with respective to joint's local coordinate system is something like that in the attached photo, where for the Elbow joint, i need to get the Elbow's rotation in the elbow's local coordinate system (i'm very grateful for you to share your ideas if i have misunderstanding about it 🙂)
      I have searched many materials on the internet about how to extract the local joint's information from FBX, the most relative one i found is the pivot rotation( and geometric transformation, object offset transformation). I'm a beginner in computer graphics, and i'm confused about whether the pivot rotation( or geometric transformation, object offset transformation) is exactly the joint's local rotation i'm seeking? I hope someone that have any ideas can help me, I'd be very grateful for any pointers in the right direction. Thanks in advance! 

    • By nOoNEE
      hello guys , i have some questions  what does glLinkProgram  and  glBindAttribLocation do?  i searched but there wasnt any good resource 
    • By owenjr
      Hi, I'm a Multimedia Engineering student. I am about to finish my dergree and I'm already thinking about what topic to cover in my final college project.
      I'm interested in the procedural animation with c++ and OpenGL of creatures, something like a spider for example. Can someone tell me what are the issues I should investigate to carry it out? I understand that it has some dependence on artificial intelligence but I do not know to what extent. Can someone help me to find information about it? Thank you very much.
       
      Examples: 
      - Procedural multi-legged walking animation
      - Procedural Locomotion of Multi-Legged Characters in Dynamic Environments
    • By Lewa
      So, i'm still on my quest to unterstanding the intricacies of HDR and implementing this into my engine. Currently i'm at the step to implementing tonemapping. I stumbled upon this blogposts:
      http://filmicworlds.com/blog/filmic-tonemapping-operators/
      http://frictionalgames.blogspot.com/2012/09/tech-feature-hdr-lightning.html
      and tried to implement some of those mentioned tonemapping methods into my postprocessing shader.
      The issue is that none of them creates the same results as shown in the blogpost which definitely has to do with the initial range in which the values are stored in the HDR buffer. For simplicity sake i store the values between 0 and 1 in the HDR buffer (ambient light is 0.3, directional light is 0.7)
      This is the tonemapping code:
      vec3 Uncharted2Tonemap(vec3 x) { float A = 0.15; float B = 0.50; float C = 0.10; float D = 0.20; float E = 0.02; float F = 0.30; return ((x*(A*x+C*B)+D*E)/(x*(A*x+B)+D*F))-E/F; } This is without the uncharted tonemapping:
      This is with the uncharted tonemapping:
      Which makes the image a lot darker.
      The shader code looks like this:
      void main() { vec3 color = texture2D(texture_diffuse, vTexcoord).rgb; color = Uncharted2Tonemap(color); //gamma correction (use only if not done in tonemapping code) color = gammaCorrection(color); outputF = vec4(color,1.0f); } Now, from my understanding is that tonemapping should bring the range down from HDR to 0-1.
      But the output of the tonemapping function heavily depends on the initial range of the values in the HDR buffer. (You can't expect to set the sun intensity the first time to 10 and the second time to 1000 and excpect the same result if you feed that into the tonemapper.) So i suppose that this also depends on the exposure which i have to implement?
      To check this i plotted the tonemapping curve:
      You can see that the curve goes only up to around to a value of 0.21 (while being fed a value of 1) and then basically flattens out. (which would explain why the image got darker.)
       
      My guestion is: In what range should the values in the HDR buffer be which then get tonemapped? Do i have to bring them down to a range of 0-1 by multiplying with the exposure?
      For example, if i increase the values of the light by 10 (directional light would be 7 and ambient light 3) then i would need to divide HDR values by 10 in order to get a value range of 0-1 which then could be fed into the tonemapping curve. Is that correct?
    • By nOoNEE
      i am reading this book : link
      in the OpenGL Rendering Pipeline section there is a picture like this: link
      but the question is this i dont really understand why it is necessary to turn pixel data in to fragment and then fragment into pixel could please give me a source or a clear Explanation that why it is necessary ? thank you so mu
       
       
    • By Inbar_xz
      I'm using the OPENGL with eclipse+JOGL.
      My goal is to create movement of the camera and the player.
      I create main class, which create some box in 3D and hold 
      an object of PlayerAxis.
      I create PlayerAxis class which hold the axis of the player.
      If we want to move the camera, then in the main class I call to 
      the func "cameraMove"(from PlayerAxis) and it update the player axis.
      That's work good.
      The problem start if I move the camera on 2 axis, 
      for example if I move with the camera right(that's on the y axis)
      and then down(on the x axis) -
      in some point the move front is not to the front anymore..
      In order to move to the front, I do
      player.playerMoving(0, 0, 1);
      And I learn that in order to keep the front move, 
      I need to convert (0, 0, 1) to the player axis, and then add this.
      I think I dont do the convert right.. 
      I will be glad for help!

      Here is part of my PlayerAxis class:
       
      //player coordinate float x[] = new float[3]; float y[] = new float[3]; float z[] = new float[3]; public PlayerAxis(float move_step, float angle_move) { x[0] = 1; y[1] = 1; z[2] = -1; step = move_step; angle = angle_move; setTransMatrix(); } public void cameraMoving(float angle_step, String axis) { float[] new_x = x; float[] new_y = y; float[] new_z = z; float alfa = angle_step * angle; switch(axis) { case "x": new_z = addVectors(multScalar(z, COS(alfa)), multScalar(y, SIN(alfa))); new_y = subVectors(multScalar(y, COS(alfa)), multScalar(z, SIN(alfa))); break; case "y": new_x = addVectors(multScalar(x, COS(alfa)), multScalar(z, SIN(alfa))); new_z = subVectors(multScalar(z, COS(alfa)), multScalar(x, SIN(alfa))); break; case "z": new_x = addVectors(multScalar(x, COS(alfa)), multScalar(y, SIN(alfa))); new_y = subVectors(multScalar(y, COS(alfa)), multScalar(x, SIN(alfa))); } x = new_x; y = new_y; z = new_z; normalization(); } public void playerMoving(float x_move, float y_move, float z_move) { float[] move = new float[3]; move[0] = x_move; move[1] = y_move; move[2] = z_move; setTransMatrix(); float[] trans_move = transVector(move); position[0] = position[0] + step*trans_move[0]; position[1] = position[1] + step*trans_move[1]; position[2] = position[2] + step*trans_move[2]; } public void setTransMatrix() { for (int i = 0; i < 3; i++) { coordiTrans[0][i] = x[i]; coordiTrans[1][i] = y[i]; coordiTrans[2][i] = z[i]; } } public float[] transVector(float[] v) { return multiplyMatrixInVector(coordiTrans, v); }  
      and in the main class i have this:
       
      public void keyPressed(KeyEvent e) { if (e.getKeyCode()== KeyEvent.VK_ESCAPE) { System.exit(0); //player move } else if (e.getKeyCode()== KeyEvent.VK_W) { //front //moveAmount[2] += -0.1f; player.playerMoving(0, 0, 1); } else if (e.getKeyCode()== KeyEvent.VK_S) { //back //moveAmount[2] += 0.1f; player.playerMoving(0, 0, -1); } else if (e.getKeyCode()== KeyEvent.VK_A) { //left //moveAmount[0] += -0.1f; player.playerMoving(-1, 0, 0); } else if (e.getKeyCode()== KeyEvent.VK_D) { //right //moveAmount[0] += 0.1f; player.playerMoving(1, 0, 0); } else if (e.getKeyCode()== KeyEvent.VK_E) { //moveAmount[0] += 0.1f; player.playerMoving(0, 1, 0); } else if (e.getKeyCode()== KeyEvent.VK_Q) { //moveAmount[0] += 0.1f; player.playerMoving(0, -1, 0); //camera move } else if (e.getKeyCode()== KeyEvent.VK_I) { //up player.cameraMoving(1, "x"); } else if (e.getKeyCode()== KeyEvent.VK_K) { //down player.cameraMoving(-1, "x"); } else if (e.getKeyCode()== KeyEvent.VK_L) { //right player.cameraMoving(-1, "y"); } else if (e.getKeyCode()== KeyEvent.VK_J) { //left player.cameraMoving(1, "y"); } else if (e.getKeyCode()== KeyEvent.VK_O) { //right round player.cameraMoving(-1, "z"); } else if (e.getKeyCode()== KeyEvent.VK_U) { //left round player.cameraMoving(1, "z"); } }  
      finallt found it.... i confused with the transformation matrix row and col. thanks anyway!
    • By Lewa
      So, i'm currently trying to implement an SSAO shader from THIS tutorial and i'm running into a few issues here.
      Now, this SSAO method requires view space positions and normals. I'm storing the normals in my deferred renderer in world-space so i had to do a conversion and reconstruct the position from the depth buffer.
      And something there goes horribly wrong (which has probably to do with worldspace to viewspace transformations).
      (here is the full shader source code if someone wants to take a look at it)
      Now, i suspect that the normals are the culprit.
      vec3 normal = ((uNormalViewMatrix*vec4(normalize(texture2D(sNormals, vTexcoord).rgb),1.0)).xyz); "sNormals" is a 2D texture which stores the normals in world space in a RGB FP16 buffer.
      Now i can't use the camera viewspace matrix to transform the normals into viewspace as the cameras position isn't set at (0,0,0), thus skewing the result.
      So what i did is to create a new viewmatrix specifically for this normal without the position at vec3(0,0,0);
      //"camera" is the camera which was used for rendering the normal buffer renderer.setUniform4m(ressources->shaderSSAO->getUniform("uNormalViewMatrix"), glmExt::createViewMatrix(glm::vec3(0,0,0),camera.getForward(),camera.getUp())//parameters are (position,forwardVector,upVector) ); Though i have the feeling this is the wrong approach. Is this right or is there a better/correct way of transforming a world space normal into viewspace?
    • By HawkDeath
      Hi,
      I'm trying mix two textures using own shader system, but I have a problem (I think) with uniforms.
      Code: https://github.com/HawkDeath/shader/tree/test
      To debug I use RenderDocs, but I did not receive good results. In the first attachment is my result, in the second attachment is what should be.
      PS. I base on this tutorial https://learnopengl.com/Getting-started/Textures.


    • By norman784
      I'm having issues loading textures, as I'm clueless on how to handle / load images maybe I missing something, but the past few days I just google a lot to try to find a solution. Well theres two issues I think, one I'm using Kotlin Native (EAP) and OpenGL wrapper / STB image, so I'm not quite sure wheres the issue, if someone with more experience could give me some hints on how to solve this issue?
      The code is here, if I'm not mistaken the workflow is pretty straight forward, stbi_load returns the pixels of the image (as char array or byte array) and you need to pass those pixels directly to glTexImage2D, so a I'm missing something here it seems.
      Regards
    • By Hashbrown
      I've noticed in most post processing tutorials several shaders are used one after another: one for bloom, another for contrast, and so on. For example: 
      postprocessing.quad.bind() // Effect 1 effect1.shader.bind(); postprocessing.texture.bind(); postprocessing.quad.draw(); postprocessing.texture.unbind(); effect1.shader.unbind(); // Effect 2 effect2.shader.bind(); // ...and so on postprocessing.quad.unbind() Is this good practice, how many shaders can I bind and unbind before I hit performance issues? I'm afraid I don't know what the good practices are in open/webGL regarding binding and unbinding resources. 
      I'm guessing binding many shaders at post processing is okay since the scene has already been updated and I'm just working on a quad and texture at that moment. Or is it more optimal to put shader code in chunks and bind less frequently? I'd love to use several shaders at post though. 
      Another example of what I'm doing at the moment:
      1) Loop through GameObjects, bind its phong shader (send color, shadow, spec, normal samplers), unbind all.
      2) At post: bind post processor quad, and loop/bind through different shader effects, and so on ...
      Thanks all! 
  • Advertisement
  • Popular Now

  • Forum Statistics

    • Total Topics
      631395
    • Total Posts
      2999780
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!