Sign in to follow this  
OrangyTang

OpenGL Colourise greyscale without shaders

Recommended Posts

OrangyTang    1298
Is it possible to colourise a texture on hardware without shader support (specifically, GF1 and GF2 era cards and up)? Hopefully in a vendor-independant (OpenGL) way? More specifically, applying a 1d colour gradient to a greyscale 2d texture, where the grey intensity converts to a colour from the gradient. I think I might be able to do something similar with palleted textures, but I don't know how much support they get (and I hear they're being phased out).

Share this post


Link to post
Share on other sites
SimmerD    1210
I'd stay away from palettes, but there is a way to do 7-bit grayscale on gf1+, at least in directx.

The easiest way is just to calculate your whole scene in color, then copy the back buffer to a texture, then apply a simple operation to the texture to display it.

The idea is to do, in ps.1.1 syntax

ps_1_1

def c0 0.29, 0.59, 0.12, 0.0 // luminance constants

tex t0 // fetch color scene

dp3 r0, t0, c0

I'm not sure if there is a simple opengl extension that does dot products...

Share this post


Link to post
Share on other sites
OrangyTang    1298
Further investigation shows that palettes are unusable in OpenGL unfortunatly (ATi don't support them, nVidia are dropping support in FX cards).

SimmerD: I want to go the other way to that - the input of a greyscale texture gets coloured according to the colour gradient on the 1d texture. I suspect theres no way to do this other than a dependant texture read, so I might be screwed for any hardware <GF3.

Share this post


Link to post
Share on other sites
Mastaba    761
Well, you are not totally screwed. You could still very easily modulate the greyscale texture with the gradient texture. And do it in one pass on all but the oldest hardware. To get the best effect, you may have to change from a simple 1D gradient to a 2D gradient.

Share this post


Link to post
Share on other sites
OrangyTang    1298
A simple modulate won't get the effect I'm after - and if I move to a 2d 'gradient' then I could of just gone for a pre-baked 2d texture. [razz]

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 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
    • By dpadam450
      FINALLY, upgrading my engine to openGL 4. I was having some trouble so I started with a stripped down application and was wondering if VAO's are required, because I have a sample working, but if I remove the VAO then it doesn't seem to like drawing my triangle.
  • Popular Now