Sign in to follow this  
boli

OpenGL get translation values back from Matrix operation

Recommended Posts

boli    100
Hello,

I am hoping someone expert at matrix transformations can help me. I have an openGL app where I have a scene set up, and I allow the user to 'twist' rotate around a certain point in the scene. I use these calls to do it:


glPushMatrix();

glLoadMatrixf((GLfloat *)currentRotationMatrix);

glScalef(defaultWorldScale,defaultWorldScale,defaultWorldScale);
glScalef(drawScale,drawScale,drawScale);
glTranslatef(xTrans, yTrans, zTrans);
glTranslatef(twistx, twisty, twistz);

glGetFloatv(GL_MODELVIEW_MATRIX, TempRotationMatrix);
glRotatef(-zr, ((float *)TempRotationMatrix)[2], ((float *)TempRotationMatrix)[6], ((float *)TempRotationMatrix)[10]);

glTranslatef(-twistx, -twisty, -twistz);
glTranslatef(-xTrans, -yTrans, -zTrans);
glScalef(1.0/drawScale,1.0/drawScale,1.0/drawScale);
glScalef(1.0/defaultWorldScale,1.0/defaultWorldScale,1.0/defaultWorldScale);


glGetFloatv(GL_MODELVIEW_MATRIX, (GLfloat *)currentRotationMatrix); // save for later

glPopMatrix();

So, I have a currentRotationMatrix and then the other transforms are to get it out to a point in space where I want to do the twist. Then I do it and reverse my setup transformations.

This works, but what I end up with is a rotationMatrix that has been dirtied with extra translation values. I want to keep my rotationMatrix as only rotations. Is there any way to take the translation values that appear in my final matrix and incorporate them into my translation values xTrans yTrans zTrans? I have experimented but cannot figure out how to do it.

I know that the bottom left three values are translation, but I can't seem to get them separated so that I can just incorporate them into my main three translation values. For example, I would have thought I could take them and divide by (defaultWorldScale*drawScale), but it doesn't work.

I hope this question makes sense -- basically I try to compose my scene from xyz translation variables and XYZ euler rotation variables. But when I interactively make changes, I don't quite know how to separate them back out.

Thanks for any advice
Bob

Share this post


Link to post
Share on other sites
dpadam450    2357
So you have any number of rotation,translation,scale in any order called multiple times, and at the end you want the position of final translation right?

If this is the case, you need to perform your final matrix on a single point (origin of your model) and then use that new point as your translate to.

If you want the final orientation you would have to take 3 other points, so:

zero, zero + x vector, zero + y vector, zero + z vector. If you on the cpu multiply those points by your final matrix, you will have the translation of where the origin of your model was. Take the transformed x vector and subtract from your transformed zero and you have the new x-axis for you matrix/orientation. And so on..

Share this post


Link to post
Share on other sites
boli    100
Hello, thanks for your reply.

I don't really have "any number" of transformations. As you can see, I have a two scale values and two sets of translations. I do these, then perform my rotation, and then UNDO the first transformations. So that what I am left with is a rotation around some point in space.

If I do as you say and perform the final matrix on my origin, then I just get the translation values of the final matrix -- ie, the three values along the bottom left row of the matrix.

But I want to know how much I need to change xTrans, yTrans, and zTrans above so that I get the same final result. I guess I should show that this is how I normally put these values together, every frame:


glMultMatrixf((GLfloat*)currentRotationMatrix);

glScalef(defaultWorldScale,defaultWorldScale,defaultWorldScale);
glScalef(drawScale,drawScale,drawScale);

glTranslatef(xTrans, yTrans, zTrans);


So normally I have a rotation-only matrix, two scales, and a set of XYZ translations. But then interactively I am rotating the model as in my first post, and I end up with a currentRotationMatrix that has the correct rotation values but that also has some extra translations. I want to extract those back to my xTrans, yTrans, zTrans. I don't really understand why it isn't just a scale by my scale values, but that doesn't seem to work.

Bob

Share this post


Link to post
Share on other sites
boli    100
I got this to work. It was almost what I was assuming, that the resultant translation values would just need to be scaled by the reverse of my original scales. What I was missing was that the translation values in the final matrix were actually rotated by the matrix's own rotation. I needed to undo that first.

So I had to zero out the translation values, invert the matrix, and rotate those values using the invert:

sgVec4 p,w;

float sfactor = 1.0/(defaultWorldScale*drawScale);

p[0] = currentRotationMatrix[12]; // translation values of final 'dirty' rotation matrix
p[1] = currentRotationMatrix[13];
p[2] = currentRotationMatrix[14];

currentRotationMatrix[12] = currentRotationMatrix[13] = currentRotationMatrix[14] = 0.0; // set them to zero

OpenGL_Invert((GLfloat *)currentRotationMatrix, (GLfloat *)currentRotationMatrixInvert);

ConcatVector(p,(GLfloat *)currentRotationMatrixInvert, w);

xTrans += w[0]*sfactor;
yTrans += w[1]*sfactor;
zTrans += w[2]*sfactor;

Bob

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      Question:
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
       
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
    • By markshaw001
      Hi i am new to this forum  i wanted to ask for help from all of you i want to generate real time terrain using a 32 bit heightmap i am good at c++ and have started learning Opengl as i am very interested in making landscapes in opengl i have looked around the internet for help about this topic but i am not getting the hang of the concepts and what they are doing can some here suggests me some good resources for making terrain engine please for example like tutorials,books etc so that i can understand the whole concept of terrain generation.
       
    • By KarimIO
      Hey guys. I'm trying to get my application to work on my Nvidia GTX 970 desktop. It currently works on my Intel HD 3000 laptop, but on the desktop, every bind textures specifically from framebuffers, I get half a second of lag. This is done 4 times as I have three RGBA textures and one depth 32F buffer. I tried to use debugging software for the first time - RenderDoc only shows SwapBuffers() and no OGL calls, while Nvidia Nsight crashes upon execution, so neither are helpful. Without binding it runs regularly. This does not happen with non-framebuffer binds.
      GLFramebuffer::GLFramebuffer(FramebufferCreateInfo createInfo) { glGenFramebuffers(1, &fbo); glBindFramebuffer(GL_FRAMEBUFFER, fbo); textures = new GLuint[createInfo.numColorTargets]; glGenTextures(createInfo.numColorTargets, textures); GLenum *DrawBuffers = new GLenum[createInfo.numColorTargets]; for (uint32_t i = 0; i < createInfo.numColorTargets; i++) { glBindTexture(GL_TEXTURE_2D, textures[i]); GLint internalFormat; GLenum format; TranslateFormats(createInfo.colorFormats[i], format, internalFormat); // returns GL_RGBA and GL_RGBA glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, createInfo.width, createInfo.height, 0, format, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, textures[i], 0); } if (createInfo.depthFormat != FORMAT_DEPTH_NONE) { GLenum depthFormat; switch (createInfo.depthFormat) { case FORMAT_DEPTH_16: depthFormat = GL_DEPTH_COMPONENT16; break; case FORMAT_DEPTH_24: depthFormat = GL_DEPTH_COMPONENT24; break; case FORMAT_DEPTH_32: depthFormat = GL_DEPTH_COMPONENT32; break; case FORMAT_DEPTH_24_STENCIL_8: depthFormat = GL_DEPTH24_STENCIL8; break; case FORMAT_DEPTH_32_STENCIL_8: depthFormat = GL_DEPTH32F_STENCIL8; break; } glGenTextures(1, &depthrenderbuffer); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); glTexImage2D(GL_TEXTURE_2D, 0, depthFormat, createInfo.width, createInfo.height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthrenderbuffer, 0); } if (createInfo.numColorTargets > 0) glDrawBuffers(createInfo.numColorTargets, DrawBuffers); else glDrawBuffer(GL_NONE); if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) std::cout << "Framebuffer Incomplete\n"; glBindFramebuffer(GL_FRAMEBUFFER, 0); width = createInfo.width; height = createInfo.height; } // ... // FBO Creation FramebufferCreateInfo gbufferCI; gbufferCI.colorFormats = gbufferCFs.data(); gbufferCI.depthFormat = FORMAT_DEPTH_32; gbufferCI.numColorTargets = gbufferCFs.size(); gbufferCI.width = engine.settings.resolutionX; gbufferCI.height = engine.settings.resolutionY; gbufferCI.renderPass = nullptr; gbuffer = graphicsWrapper->CreateFramebuffer(gbufferCI); // Bind glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo); // Draw here... // Bind to textures glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textures[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, textures[1]); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textures[2]); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); Here is an extract of my code. I can't think of anything else to include. I've really been butting my head into a wall trying to think of a reason but I can think of none and all my research yields nothing. Thanks in advance!
    • By Adrianensis
      Hi everyone, I've shared my 2D Game Engine source code. It's the result of 4 years working on it (and I still continue improving features ) and I want to share with the community. You can see some videos on youtube and some demo gifs on my twitter account.
      This Engine has been developed as End-of-Degree Project and it is coded in Javascript, WebGL and GLSL. The engine is written from scratch.
      This is not a professional engine but it's for learning purposes, so anyone can review the code an learn basis about graphics, physics or game engine architecture. Source code on this GitHub repository.
      I'm available for a good conversation about Game Engine / Graphics Programming
    • By C0dR
      I would like to introduce the first version of my physically based camera rendering library, written in C++, called PhysiCam.
      Physicam is an open source OpenGL C++ library, which provides physically based camera rendering and parameters. It is based on OpenGL and designed to be used as either static library or dynamic library and can be integrated in existing applications.
       
      The following features are implemented:
      Physically based sensor and focal length calculation Autoexposure Manual exposure Lense distortion Bloom (influenced by ISO, Shutter Speed, Sensor type etc.) Bokeh (influenced by Aperture, Sensor type and focal length) Tonemapping  
      You can find the repository at https://github.com/0x2A/physicam
       
      I would be happy about feedback, suggestions or contributions.

  • Popular Now