Sign in to follow this  

OpenGL Why does glm::scale move my mesh?

This topic is 1837 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

I have a mesh to which I apply Scale.

Here's before I apply scale to the cube behind:

http://s7.postimage.org/r25iv2s0r/1png.png

And here's after:

http://s2.postimage.org/6qfk75ul5/image.png

The cube scaled correctly, but why did the cube move?

Here's the code for rendering it:
 

 void OpenGLRenderer::RenderMesh(MeshPtr mesh, const Mat4& modelMatrix, const Mat4& viewMatrix, const Mat4& projectionMatrix)
    {
        if (mesh)
        {
            // upload MVP matrix
            Mat4 MVP = projectionMatrix * viewMatrix * modelMatrix;    // modelMatrix is a Mat4(1.0f) that has been applied glm::scale(Mat4(1.0f), Vec3(2.0f, 1.0f, 1.0f))
            ShaderData shaderData;
            shaderData.Color.x = 1.0f; shaderData.Color.y = 0.5f; shaderData.Color.z = 0.5f; shaderData.Color.w = 1.0f;
            shaderData.MVPMatrix = MVP;
            mUniBuffer.SetData(shaderData);

            // render
            mesh->GetVertexBuffer()->Render();
        }
    }

 

 



What could be wrong?

EDIT: I can note that if I do translate instead of scale, the cube would move as expected

Edited by KaiserJohan

Share this post


Link to post
Share on other sites

If there are no explicit translations anywhere, then: what are the coordinates of the vertices of the cube?

 

Consider, for example, that the cube spans the axis-aligned coordinates from (1, 1, 1) to (2, 2, 2). That is, a unit-sized cube centered at (1.5, 1.5, 1.5). Now scale the X-axis by 2, and the cube now spans the coordinates (2, 1, 1) to (4, 2, 2). As you can see, the size of the cube has been scaled by 2, but so has its center which is now at (3, 1.5, 1.5). This is not an additional translation, but an inherent effect of the scaling: scaling happens around the origin, and if your cube's center-of-scaling is not at the origin, the offset from the origin will also be scaled accordingly.

Share this post


Link to post
Share on other sites

Here's the vertex data and vertex indices:

 

const float vertexPositions1[] =
        {
            // front vertices
            -4.0f, -5.5f, -20.0f,
            -4.5f, -5.5f, -20.0f,
            -4.5f, -5.0f, -20.0f,
            -4.0f, -5.0f, -20.0f,

            // back vertices
            -4.0f, -5.5f, -20.5f,
            -4.5f, -5.5f, -20.5f,
            -4.5f, -5.0f, -20.5f,
            -4.0f, -5.0f, -20.5f
        };
 

        const uint16_t indexData1[] =
        {
            // back
            5, 4, 7,
            5, 7, 6,

            // right
            1, 5, 6,
            1, 6, 2,

            // left
            0, 4, 7,
            0, 7, 3,

            // top
            5, 4, 0,
            5, 0, 1,

            // bottom
            6, 7, 3,
            6, 3, 2,

            // front
            1, 0, 3,
            1, 3, 2
        };

Share this post


Link to post
Share on other sites

That just proves what Brother Bob said.

 

You could translate it to the origin, scale, translate it back to where it should be.

Or even better just have all your model coordinates around the origin, then scale and translate to where it should be.

Share this post


Link to post
Share on other sites

Centered around the origin; like this?

 

// front vertices
1.0f, -1.0f, 1.0f,           // bottom right
-1.0f, -1.0f, 1.0f,          // bottom left
-1.0f, 1.0f, 1.0f,          // top left
1.0f, 1.0f, 1.0f,            // top right
 
// back vertices
1.0f, -1.0f, -1.0f,           // bottom right
-1.0f, -1.0f, -1.0f,          // bottom left
-1.0f, 1.0f, -1.0f,          // top left
1.0f, 1.0f, -1.0f,            // top right

Share this post


Link to post
Share on other sites
For a flying cube it would be good to have the center of the cube at origin. For things on ground it may be easier if the center of the bottom surface is on origin or one of the bottom corners depending on how it is easier for you to place it somewhere. Edited by wintertime

Share this post


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

  • Similar Content

    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glUseProgram(program.get());
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glUseProgram(0);
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
      glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
       
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
    • By dpadam450
      I have this code below in both my vertex and fragment shader, however when I request glGetUniformLocation("Lights[0].diffuse") or "Lights[0].attenuation", it returns -1. It will only give me a valid uniform location if I actually use the diffuse/attenuation variables in the VERTEX shader. Because I use position in the vertex shader, it always returns a valid uniform location. I've read that I can share uniforms across both vertex and fragment, but I'm confused what this is even compiling to if this is the case.
       
      #define NUM_LIGHTS 2
      struct Light
      {
          vec3 position;
          vec3 diffuse;
          float attenuation;
      };
      uniform Light Lights[NUM_LIGHTS];
       
       
    • By pr033r
      Hello,
      I have a Bachelor project on topic "Implenet 3D Boid's algorithm in OpenGL". All OpenGL issues works fine for me, all rendering etc. But when I started implement the boid's algorithm it was getting worse and worse. I read article (http://natureofcode.com/book/chapter-6-autonomous-agents/) inspirate from another code (here: https://github.com/jyanar/Boids/tree/master/src) but it still doesn't work like in tutorials and videos. For example the main problem: when I apply Cohesion (one of three main laws of boids) it makes some "cycling knot". Second, when some flock touch to another it scary change the coordination or respawn in origin (x: 0, y:0. z:0). Just some streng things. 
      I followed many tutorials, change a try everything but it isn't so smooth, without lags like in another videos. I really need your help. 
      My code (optimalizing branch): https://github.com/pr033r/BachelorProject/tree/Optimalizing
      Exe file (if you want to look) and models folder (for those who will download the sources):
      http://leteckaposta.cz/367190436
      Thanks for any help...

  • Popular Now