How do you set the Bounds of glm::ortho based on scene max and min coordinates?

Question

I have a triangle and have 3 vertices anywhere in space.

I attempted to get the max and min coordinates for it.

void findBoundingBox(glm::vec3 & minBB, glm::vec3 & maxBB)
{
        minBB.x = std::min(minBB.x, mCoordinate.x);  
        minBB.y = std::min(minBB.y, mCoordinate.y);
        minBB.z = std::min(minBB.z, mCoordinate.z);
        maxBB.x = std::max(maxBB.x, mCoordinate.x);
        maxBB.y = std::max(maxBB.y, mCoordinate.y);
        maxBB.z = std::max(maxBB.z, mCoordinate.z);
    }
}

Now I tried to set :

glm::vec3 InverseViewDirection(50.0f, 200, 200);  //Inverse View Direction
glm::vec3 LookAtPosition(0.0,0,0); // I can make it anywhere with barycentric coord, but this is the simple case
glm::vec3 setupVector(0.0, 1, 0);

I tried to set the orthographic view to wrap the triangle by:

myCamera.setProjectionMatrix(min.x, max.x, max.y,min.y, 0.0001f, 10000.0f);

But its not neatly bounding the triangle in my view.

I've been stumped on this for a day, any pointers?

Bad: output : (I want the view to neatly bound the triangle)

Edit:

Based on a comment ( I have tried to update the bounds with the view matrix (model is identity, so ignoring that for now) still no luck :(

glm::vec4 minSS = ((myCamera.getViewMatrix()) * glm::vec4(minWS, 0.0));
glm::vec4 maxSS = ((myCamera.getViewMatrix()) * glm::vec4(maxWS, 0.0));

myCamera.setProjectionMatrix(minSS.x, maxSS.x, maxSS.y, minSS.y, -200.0001f, 14900.0f);

Answer 1

You will need to apply all transformations that come before the perspective transformation to your input points when you calculate the bounding box.

In your code fragments, it looks like you're applying a viewing transform with an arbitrary viewpoint (50, 200, 200) as part of your rendering. You need to apply this same transformation to your input points before you feed them into your findBoundingBox() function.

In more mathematical terms, you typically have something like this in your vertex shader, with InputPosition being the original vertex coordinates:

gl_Position = ProjectionMatrix * ViewMatrix * ModelMatrix * InputPosition;

To determine a projection matrix that will map all your points to a given range, you need to look at all points that the projection matrix is applied to. With the notation above, those points are ViewMatrix * ModelMatrix * InputPosition. So when you calculate the bounding box, the model and view matrices (or the modelview matrix if you combine them) needs to be applied to the input points.