Sign in to follow this  
oliver_mpt

OpenGL Newbie color question

Recommended Posts

oliver_mpt    100
Hello ! I'm new to DirectX, coming from OpenGL. I've noticed that 3D objects must have a color parameter for each vertex. In the case of an object with uniform color, I would like to change its color, in order to redraw it several times with different colors. Is there a way without changing the color in all vertices ? it seems pretty inneficient to me. In particular, we have the option to store the vertex and index buffers in different memories to optimize loading speed. In that case accessing to all vertices to change color is particularly not efficient. Is there something like glColor in OpenGL that allow me to change the current color - DO I need absolutely to store it in ALL vertex ? regards, Olivier

Share this post


Link to post
Share on other sites
undead    368
Are you referring to the fixed function pipeline?

IMHO the best solution is to write a simple shader.
Don't use the vertex color, set a float4 parameter and in the pixel shader just output that color.

Share this post


Link to post
Share on other sites
GregMichael    135
You don't *have* to have colour per vertex, unless you are using the fixed function pipeline to render with. You could have a vertex structure like this...

float x, y, z; // Position
float nx, ny, nz; // Normal

And then use a shader to render with what ever colour you like.

If you *are* using the FFP then I think the only way is with vertex format...

float x, y, z; // Position
float nx, ny, nz; // Normal
DWORD colour; // Colour

Which means changing each vertex colour before rendering - which shouldn't be a major problem depending on how many vertices you are dealing with.

For the most efficient way, I think go the shader route - FFP rendering is becoming obsolete.

Share this post


Link to post
Share on other sites
kauna    2922
Hi,

With FFP you can use the material parameters to change the object color. No need to have per-vertex color.

Cheers!

Share this post


Link to post
Share on other sites
oliver_mpt    100
Hello

Thanks for all the answers,

I'm not sure I unsderstand, though.
doest it read FFP = directX9 and shader route = DX10 ?

I need absolutely Windows XP compatibility, so as far as I understand no DX10.

can you clarify a bit for me ? (I told you: newbie question ;-))

Oliver

Share this post


Link to post
Share on other sites
Tom KQT    1704
Quote:

I'm not sure I unsderstand, though.
doest it read FFP = directX9 and shader route = DX10 ?

Not exactly.

DirectX9 = FFP or shaders, depends on what you decide to use.
DirectX10 = shaders, there's no FFP.

Share this post


Link to post
Share on other sites
ET3D    810
For D3D9, I'd suggest using pixel shaders whether you use FFP or shaders for the vertices. They're simply a lot easier to understand and program than texture stages.

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 Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
       
      Thanks
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
    • By Picpenguin
      Hi
      I'm new to learning OpenGL and still learning C. I'm using SDL2, glew, OpenGL 3.3, linmath and stb_image.
      I started following through learnopengl.com and got through it until I had to load models. The problem is, it uses Assimp for loading models. Assimp is C++ and uses things I don't want in my program (boost for example) and C support doesn't seem that good.
      Things like glVertexAttribPointer and shaders are still confusing to me, but I have to start somewhere right?
      I can't seem to find any good loading/rendering tutorials or source code that is simple to use and easy to understand.
      I have tried this for over a week by myself, searching for solutions but so far no luck. With tinyobjloader-c and project that uses it, FantasyGolfSimulator, I was able to actually load the model with plain color (always the same color no matter what I do) on screen and move it around, but cannot figure out how to use textures or use its multiple textures with it.
      I don't ask much: I just want to load models with textures in them, maybe have lights affect them (directional spotlight etc). Also, some models have multiple parts and multiple textures in them, how can I handle those?
      Are there solutions anywhere?
      Thank you for your time. Sorry if this is a bit confusing, English isn't my native language
  • Popular Now