• Advertisement
Sign in to follow this  

OpenGL Understanding Matrices in a 3d world

This topic is 4636 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

http://www.devmaster.net/articles/viewing-systems/ I've been reading that and the Cameral Class tutorial on NEHE and I'm just trying to understand the theory here. Basically there is a kind of matrix in opengl that defines what opengl considers up down left right near far etc. The x, y, z. Transformations, rotations and even gluLookAt all modify the world with that original set of axis in mind. What a camera class is trying to do is load a completely new definition of the world, I imagine using glLoadMatrix or glMultMatrix. Is this the proper way of understanding how a camera will work ? Ive been using some clever calculus on gluLookAt, which transforms the world properly but leaves me with something of a "flashlight view" when what I want is a kind of "world lighting" so that I will on some occasions, see the dark side of some objects.

Share this post

Link to post
Share on other sites
Original post by harnacks
Ive been using some clever calculus on gluLookAt, which transforms the world properly but leaves me with something of a "flashlight view" when what I want is a kind of "world lighting" so that I will on some occasions, see the dark side of some objects.

WTF? Can you be a little more descriptive? Matrices have little (nothing) to do with lighting in the conceptual sense. Please post some screenshots or some code. Other than that you can "occasionally" see the the darkside if you turn on the lights/disable lighting... "occasionally"....

Share this post

Link to post
Share on other sites
As far as I know, a camera is an object that translates the SCENE so you can see the scene itself from adifferent point of view... said that, I can explain what my camera class does:
every frame, my engine updates modelview matrix, translating and rotating the scene according to camera position/rotation... obviusly, if camera moves left, the scene must be traslated on the right, and the same is for rotations: scene must be translated/rotated on the opposide side of camera position/rotation... I mean, placing the camera in (-1,0,0), moves the scene at (1,0,0)...
So, returning to your question, yes, a camera is an object that manipulates modelview matrix :P

About lights, it seems you are not updating light position after setting your camera... if you don't do that, you should see the scene like a miner with a light on the helmet :P

Share this post

Link to post
Share on other sites
I don't know of a way to move the light though.

1) I'm not sure how the math works.

2) I dont konw how to actually set a position for the light once its been enabled in the initialization.

Any thoughts ?

Share this post

Link to post
Share on other sites
Original post by BladeWise
1. Really really bad! :P
2. In the same way you initialize it... Oo

Quoted for truth.

Matrices aren't all that easy to understand. I know where you are coming from. Basicly though, the light position get moved witht the rest of the world, or should anyway. So you need to set the light to its position after the camera/gluLookAt does its thing so that the light always gets to (x,y,z) in the world. If it is done before(in the init), it will always be there, and even if the camera moves, the light will be where it was. So if the light is at (0,0,1), as in right in front of the monitor shining to the world like your eyes, and you rotate the world, after putting the light, the light still stays where you put it, next to your eyes.

Share this post

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

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By LifeArtist
      Good Evening,
      I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
      First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
      I am really stucked right now because of the fundamental question:
      Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
      If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on. 
      In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
      Should I treat those debug objects as entities/components?
      For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
      Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
    • By QQemka
      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
      Thank you
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
    • By Devashish Khandelwal
      While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
      Anyone has any idea .. what should I do?
  • Advertisement