Sign in to follow this  

OpenGL FPS Camera

Recommended Posts

After writing my first FPS camera view in OpenGl, I notices a possible artifact that has confused me. I'm curious if this is a known issue... When the camera spawns, the camera is viewing in the -z direction with +x to the right and +y is up. Linear motion of the mouse in the +/-y direction generates x axis rotation and linear mouse motion in the +/-x direction generates y axis rotation. Now when I move the mouse in a circular motion on the screen, I am seeing a noticeable rotation in the z-axis. The pseudocode is pretty straight forward:

rotz = 0; // always!

//Calculate Transform matrix based on update params from the mouse and keyboard
UpdateMatrix  = CalculateEulerMatrix(x,y,z,rotx,roty,rotz);

//Update "Current" World Transform
CurrentMatrix  = UpdateCurrentMatrix(UpdateMatrix);

//Transpose Current Matrix for openGl
oMTranspose = TransposeMatrix(CurrentMatrix);

//Convert 2D array to 1D Array for OpenGl
oMReshape = MatrixReshape(oMTranspose);
//Load Matix into ModelView

I've checked the math and everything seems fine. The camera view is working as expected, but there is just this minor issue.

Share this post

Link to post
Share on other sites
I'm just going to post my code. Your rotation code is wrong for some reason. Here I have a camera with a left/right angle called side angle and up/down angle called up angle. To create the matrix: translate, rotate on the side angle, rotate on the up angle. Hope it helps.

void Input()

gCamera->z-= (cos(gCamera->side_angle*(3.14/180)))*2;
gCamera->x+= (sin(gCamera->side_angle*(3.14/180)))*2;

gCamera->z+= (cos(gCamera->side_angle*(3.14/180)))*2;
gCamera->x-= (sin(gCamera->side_angle*(3.14/180)))*2;
gCamera->x-= (cos(gCamera->side_angle*(3.14/180)))*2;
gCamera->z-= (sin(gCamera->side_angle*(3.14/180)))*2;
gCamera->x+= (cos(gCamera->side_angle*(3.14/180)))*2;
gCamera->z+= (sin(gCamera->side_angle*(3.14/180)))*2;


if(mouse.x < 400 )
if(mouse.x > 400 )

if(mouse.y > 300)
gCamera->up_angle += .6;
if(mouse.y < 300)
gCamera->up_angle -= .6;



glRotatef(cam->up_angle, 1, 0, 0);
glRotatef(cam->side_angle, 0, 1, 0);

glGetFloatv(GL_MODELVIEW_MATRIX, cam->Camera_Matrix);


Share this post

Link to post
Share on other sites
And btw, convering a 2d array to a 1d array can be done like such: I'm assuming your using glMultMatrixf( glFloat* [16] ) ?

float M_44[4][4];
float M_16[16];

M_44[0][16] , you can index like this. 0*4 steps + 16 bytes.

glMultMatrixf( &(M_44[0][0] ); <-----treated as a 4x4 array.

Its all 16*float_size bytes in memory, its all stored the same. 2d arrays are just built easier for you as a programmer.

Share this post

Link to post
Share on other sites
Its a common problem Ive seen pop up, Ive had it myself. You try and rotate the camera in a circular motion, from right, up, left, down, repeat, almost like rolling your head and you start getting roll.
Id be interested in seeing the CalculateEulerMatrix(x,y,z,rotx,roty,rotz) and
UpdateCurrentMatrix(UpdateMatrix) functions to get a better idea of how your going about this.
I dont remember the exact reason why it happens, but I remember fixing it by not updating the orientation each frame, but accumulating the angles and then rebuilding the orientation from these angles, instead of updating or modifying the old orientation with new rotation information.

Share this post

Link to post
Share on other sites
I just double checked all the math again and it seems fine. My Euler Matrix is defined as:

1 0 0 0
0 cos(rotx) sin(rotx) 0
0 -sin(rotx) cos(rotx) 0
x 0 0 1

cos(roty) 0 -sin(roty) 0
0 1 0 0
sin(roty) 0 cos(roty) 0
0 y 0 1


cos(rotz) sin(rotz) 0 0
-sin(rotz) cos(rotz) 0 0
0 0 1 0
0 0 z 1

R = RxRyRz

Based on the glTranslatef description, (x,y,z) need to be defined down the 4th column. I'm not sure about the rotation params (R), but when I transposed the matrix the camera responded correctly (x,y rotation). I followed the Matrix index definition from the glLoadMatrix description, so I'm sure the Matrix reshape func is correct.

I'm really just trying to understand how to go from a Euler matrix to glLoadMatrix.

EDIT: The UpdateCurrentMatrix function just takes the current ModelView matrix and multiplies it by the updated Euler Matrix based on recent deltas in mouse position and key hits like so:

Current = Euler(Update) * Current;

Share this post

Link to post
Share on other sites
You are building the matrix fine, but try not using any matrix built from a previous frame, instead build a new matrix each frame straight from the angles.

float rx, ry, rz;
// each frame, get mouse movement
rx += mouseMoveAsAngleAmount; // += signed amount, -/+ mouse moves left/right
ry += mouseMoveAsAngleAmount; // += signed amount, -/+ mouse moves up/down
rz = 0;
// build new matrix from these total amounts each frame
matrix = From(rx, ry, rz)
// use new matrix built each frame, discarding old

Share this post

Link to post
Share on other sites
After testing out the camera, I noticed a few differences:

When the modelview matrix got "updated" based on my original implementation, the only issue was the z-axis rotation when moving the mouse in a circular pattern. I was able to view my world model inside and outside its boundaries and still have the feel of a camera.

Now that I'm accumulating mouse and keyboard data and calculating a new modelview matrix per frame, the camera has a different feel. Let me try to explain...

When I'm inside my world model (e.g. a simple skycube), I feel that the world model is rotating and not the camera. If I zoom out, well past the boundaries of the world model, I see the world model changing it orientation and not the camera. I'm no longer able to "fly" around the model as I did when I updated the modelview matrix. This approach seems to work while the camera is inside the world model but not outside.

The second approach seems to be an artifact of translating before rotating, but I can't explain these difference based on the implementation.

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  

  • Announcements

  • Forum Statistics

    • Total Topics
    • Total Posts
  • Similar Content

    • By test opty
      Hi all,
      I'm starting OpenGL using a tut on the Web. But at this point I would like to know the primitives needed for creating a window using OpenGL. So on Windows and using MS VS 2017, what is the simplest code required to render a window with the title of "First Rectangle", please?
    • By DejayHextrix
      Hi, New here. 
      I need some help. My fiance and I like to play this mobile game online that goes by real time. Her and I are always working but when we have free time we like to play this game. We don't always got time throughout the day to Queue Buildings, troops, Upgrades....etc.... 
      I was told to look into DLL Injection and OpenGL/DirectX Hooking. Is this true? Is this what I need to learn? 
      How do I read the Android files, or modify the files, or get the in-game tags/variables for the game I want? 
      Any assistance on this would be most appreciated. I been everywhere and seems no one knows or is to lazy to help me out. It would be nice to have assistance for once. I don't know what I need to learn. 
      So links of topics I need to learn within the comment section would be SOOOOO.....Helpful. Anything to just get me started. 
      Dejay Hextrix 
    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By aejt
      I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
      I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
      This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
      I have these classes:
      For GPU resources:
      Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
      Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
      ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).  
      And my plan is to define everything into these XML documents to abstract away files:
      Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
      Factory classes for resources:
      For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
      Factory classes for assets:
      Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).
      Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
    • By nedondev
      I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
  • Popular Now