Select object in OpenGL when doing transformations in the vertex shader
I'm pretty new to OpenGL and am trying to implement a simple program where I can draw cubes, move them around with the mouse, and delete them.
Previously I had done my drag operations by translating on the CPU. In this way I was able to use ray-tracing to pick out the element I wanted because the vertices themselves were being updated.
However, I'm trying to move all of the transformations to the GPU and in doing so realized that I would then be giving up updated access to the vertices on the CPU (as the CPU still thinks the vertices are the un-transformed ones). How does one do this communication so that I wouldn't have to manually do transformations on the CPU as well as in the Vertex Shader?
c++ opengl
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
add a comment |
I'm pretty new to OpenGL and am trying to implement a simple program where I can draw cubes, move them around with the mouse, and delete them.
Previously I had done my drag operations by translating on the CPU. In this way I was able to use ray-tracing to pick out the element I wanted because the vertices themselves were being updated.
However, I'm trying to move all of the transformations to the GPU and in doing so realized that I would then be giving up updated access to the vertices on the CPU (as the CPU still thinks the vertices are the un-transformed ones). How does one do this communication so that I wouldn't have to manually do transformations on the CPU as well as in the Vertex Shader?
c++ opengl
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
1
You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07
add a comment |
I'm pretty new to OpenGL and am trying to implement a simple program where I can draw cubes, move them around with the mouse, and delete them.
Previously I had done my drag operations by translating on the CPU. In this way I was able to use ray-tracing to pick out the element I wanted because the vertices themselves were being updated.
However, I'm trying to move all of the transformations to the GPU and in doing so realized that I would then be giving up updated access to the vertices on the CPU (as the CPU still thinks the vertices are the un-transformed ones). How does one do this communication so that I wouldn't have to manually do transformations on the CPU as well as in the Vertex Shader?
c++ opengl
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
I'm pretty new to OpenGL and am trying to implement a simple program where I can draw cubes, move them around with the mouse, and delete them.
Previously I had done my drag operations by translating on the CPU. In this way I was able to use ray-tracing to pick out the element I wanted because the vertices themselves were being updated.
However, I'm trying to move all of the transformations to the GPU and in doing so realized that I would then be giving up updated access to the vertices on the CPU (as the CPU still thinks the vertices are the un-transformed ones). How does one do this communication so that I wouldn't have to manually do transformations on the CPU as well as in the Vertex Shader?
c++ opengl
c++ opengl
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
asked Nov 19 '18 at 10:40
LivingRobotLivingRobot
366619
366619
1
You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07
add a comment |
1
You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07
1
1
You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07
You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07
add a comment |
1 Answer
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votes
No matter where you're doing your transformations, you will typically have a model matrix that describes where each object is in the scene. Instead of transforming each object into world space just so you can check for intersection with a world-space ray, you can also transform the ray into the object space of each object by transforming the ray with the inverse model matrix.
One general issue with ray-tracing is that, as your scene gets larger, brute force testing of each object will get increasingly slow. You can use acceleration structures like an Octree or a Bounding Volume Hierarchy to speed things up. A completely different approach when it comes to picking would be just render an ID buffer, i.e. a buffer that has the same resolution as your currently rendered frame and for each pixel saves the ID of the object that is visible at that pixel. Then you can simply read back the value of the pixel underneath the cursor to find out what object you hit without the need to do any raytracing. Rendering the ID buffer could be done as a separate pass or can likely just be added as an additional render target to a pass you're already doing, e.g., prefilling the depth buffer or just when rendering the scene in case you only do one pass.
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
add a comment |
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1 Answer
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No matter where you're doing your transformations, you will typically have a model matrix that describes where each object is in the scene. Instead of transforming each object into world space just so you can check for intersection with a world-space ray, you can also transform the ray into the object space of each object by transforming the ray with the inverse model matrix.
One general issue with ray-tracing is that, as your scene gets larger, brute force testing of each object will get increasingly slow. You can use acceleration structures like an Octree or a Bounding Volume Hierarchy to speed things up. A completely different approach when it comes to picking would be just render an ID buffer, i.e. a buffer that has the same resolution as your currently rendered frame and for each pixel saves the ID of the object that is visible at that pixel. Then you can simply read back the value of the pixel underneath the cursor to find out what object you hit without the need to do any raytracing. Rendering the ID buffer could be done as a separate pass or can likely just be added as an additional render target to a pass you're already doing, e.g., prefilling the depth buffer or just when rendering the scene in case you only do one pass.
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
add a comment |
No matter where you're doing your transformations, you will typically have a model matrix that describes where each object is in the scene. Instead of transforming each object into world space just so you can check for intersection with a world-space ray, you can also transform the ray into the object space of each object by transforming the ray with the inverse model matrix.
One general issue with ray-tracing is that, as your scene gets larger, brute force testing of each object will get increasingly slow. You can use acceleration structures like an Octree or a Bounding Volume Hierarchy to speed things up. A completely different approach when it comes to picking would be just render an ID buffer, i.e. a buffer that has the same resolution as your currently rendered frame and for each pixel saves the ID of the object that is visible at that pixel. Then you can simply read back the value of the pixel underneath the cursor to find out what object you hit without the need to do any raytracing. Rendering the ID buffer could be done as a separate pass or can likely just be added as an additional render target to a pass you're already doing, e.g., prefilling the depth buffer or just when rendering the scene in case you only do one pass.
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
add a comment |
No matter where you're doing your transformations, you will typically have a model matrix that describes where each object is in the scene. Instead of transforming each object into world space just so you can check for intersection with a world-space ray, you can also transform the ray into the object space of each object by transforming the ray with the inverse model matrix.
One general issue with ray-tracing is that, as your scene gets larger, brute force testing of each object will get increasingly slow. You can use acceleration structures like an Octree or a Bounding Volume Hierarchy to speed things up. A completely different approach when it comes to picking would be just render an ID buffer, i.e. a buffer that has the same resolution as your currently rendered frame and for each pixel saves the ID of the object that is visible at that pixel. Then you can simply read back the value of the pixel underneath the cursor to find out what object you hit without the need to do any raytracing. Rendering the ID buffer could be done as a separate pass or can likely just be added as an additional render target to a pass you're already doing, e.g., prefilling the depth buffer or just when rendering the scene in case you only do one pass.
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
No matter where you're doing your transformations, you will typically have a model matrix that describes where each object is in the scene. Instead of transforming each object into world space just so you can check for intersection with a world-space ray, you can also transform the ray into the object space of each object by transforming the ray with the inverse model matrix.
One general issue with ray-tracing is that, as your scene gets larger, brute force testing of each object will get increasingly slow. You can use acceleration structures like an Octree or a Bounding Volume Hierarchy to speed things up. A completely different approach when it comes to picking would be just render an ID buffer, i.e. a buffer that has the same resolution as your currently rendered frame and for each pixel saves the ID of the object that is visible at that pixel. Then you can simply read back the value of the pixel underneath the cursor to find out what object you hit without the need to do any raytracing. Rendering the ID buffer could be done as a separate pass or can likely just be added as an additional render target to a pass you're already doing, e.g., prefilling the depth buffer or just when rendering the scene in case you only do one pass.
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
edited Nov 19 '18 at 11:22
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
answered Nov 19 '18 at 11:14
Michael KenzelMichael Kenzel
4,083719
4,083719
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
add a comment |
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
Thanks so much!!! This really helped!
– LivingRobot
Nov 19 '18 at 11:44
add a comment |
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You don't need to actually transform all vertices on the CPU for ray tracing. Instead, just transform the ray (position, direction) by the inverse of that transformation.
– httpdigest
Nov 19 '18 at 11:07