Hi I'm working to create a space environment with a ship inside.But after the creation of the skybox (no errors) I put my ship inside but it hasnt colour. It's something like white-black
I did(modeled) the ship with OPENSCAD and after with MESHLAB I exported it into .OBJ format. I load it inside the source code but he hasn't the texture/colour . That my ship in Meshlab :
I need to know only I have to add something about color in the code or it's error in input. What this?
If you need I post the code, but if is somthing normal this error explain me, anyway I'm a little newbie in opengl, so be patient, thank you
EDIT :
Look my .obj file in windows:
And the same project in ubuntu :
What's this difference?
Anyway the openscad code :
module navicella(){
$fn=100;
rotate([0,180,270]){
union(){
rotate([270,180,0]){
rotate([90,0,0])
cylinder(50,7,10,center=true);
intersection(){
translate([0,-25,0])
sphere(10);
translate([0,-25,0])
cube(19,center=true);
}
difference(){
translate([0,35,0])
cube([10,15,15],center=true);
translate([0,40,0])
sphere(13);
}
translate([5,-10,0])rotate([90,0,70])
cube([35,1,15],center=true);
translate([-2,0,0])rotate([90,0,95])
cube([50,1,10],center=true);
translate([0,3,6])rotate([0,-15,90])
cube([40,1,20],center=true);
translate([0,3,-6])rotate([0,15,90])
cube([40,1,20],center=true);
translate([0,-35,0])rotate([90,0,0])
cylinder(10,5,0,center=true);
translate([0,20,0])rotate([0,90,0])
cube([45,1,2],center=true);
translate([0,25,0]) rotate([90,0,0])
cylinder(5,4,7,center=true);
}
}
}
}
navicella();
Looks like you have forgot to disable all used textures that are not used by your model. That is very common mistake (I do it all the time still today).
What is probably happening?
You rendered skybox or any object with textures
So for example GL_CUBE_MAP and or GL_TEXTURE_2D are enabled. Now when you start rendering your mesh that does not contain texture the textures are still enabled. So for every fragment/pixel GL will always sample the last set texture coordinate from last binded texture in all of the enabled texture targets and combine color according to GL settings.
So if you model does not contain texture coordinates GL will use the last set one. That is usually in corner area where black border is ... or you are just in some dark region of texture. Also if you unbind textures that only means you bind default texture 0 which is usually black.
To test/remedy this just callglDisable(GL_....); for all previously used texture targets. If it helps you know where the problem is.
Also if your object contains texture coordinates and texture is not loaded properly (like wrong file name/path) then the result is usually black.
Missing or negative normals while rendering with lighting enabled
Does not looks like it but it could be also the reason. If your model has wrong or no normals then the lighting computation result in wrong lighting. If the object is always dark even if you rotate it the the normals are negated (facing the other way) and you should change the front face for lighting/material or negate the normals.
If the color intensity is changing with rotation then your object has probably no normal and again the last set normal is used (from previous rendering). In such case either compute normals for the object (via cross product) or disable lighting for that object.
I'm using Qt5 and its OpenGL integration, and am running into a problem when I try to draw translucent objects. When an object is translucent, whatever is visible behind my OpenGL window is shown within the screen area of that object, instead of the object being blended with whatever is already in the colour buffer. I have started watching YouTube videos through my translucent objects, as whatever shows through is live.
Interestingly, the most see-through an object gets seems to occur at half opacity - full opacity renders it solid, while zero opacity renders nothing at all (and whatever was previously in the background of the 3D scene remains there). Rendering translucent objects last does not fix the issue.
I have noticed that this also happens when I enable mipmaps on my textures - as the distance to a point on an object increases, the pixel concerned becomes more translucent and displays whatever is behind the OpenGL window. The issue occurs both on my Windows and OSX machines.
Is this a known issue? Is there a workaround? Google hasn't proven too helpful.
Hah, that's a funny one. I can't tell you what is going on, because it normally takes some extra effort to make windows actually transparent; in Windows you have to select a framebuffer format with an alpha channel and call DwnEnableBlurBehindWindow to actually achieve this effect. And as far as I know Qt doesn't do this.
But if it does here are a few hints:
Make sure you clear your framebuffer to alpha=1
When rendering translucent objects keep the destination alpha value 1, i.e. don't use blending modes and functions that modify the destination alpha value, or force it to 1.
There's actually little use for the alpha channel on the main window framebuffer, except for implementing window translucency effects. Unless you need those you should choose an either pixel format without an alpha channel for your window framebuffer, or keep all its pixels alpha values at full opacity.
I am wondering what kind of methods are commonly used when we do zoom in/out.
In my current project, I have to display millions of 2D rectangles on the screen, and I am using a fixed viewport and changing glortho2D variables when I have to zoom in/out.
I am wondering if this is a good way of doing it and what other solution can I use.
I also have another question which I think it is related to
how should I do zoom in/out.
As I said, I am currenly using a fixed viewport and changing glortho2D variables in my code, and I assumed that opengl will be able to figure out which rectangles are out of the screen and not render them. However, it seems like opengl is redrawing all the rectangles again and again. The rendering time of viewing millions of rectangles (zoom out) is equal to vewing hundreds of rectangles (zoom into a particular area), which is opposite of what I expected. I am wondering if it is related to the zooming methods I used or am I missing something important.
ie . I am using VBO while rendering the rectangles.
and I assumed that opengl will be able to figure out which rectangles are out of the screen
You assumed wrong
and not render them.
OpenGL is a rather dumb drawing API. There's no such thing like a scene in OpenGL. All it does is coloring pixels on the framebuffer one point, line or triangle at a time. When geometry lies outside the viewport it still has to be processed up to the point it gets clipped (and then discarded).
I'm trying to implement a navigation technique for 3D scenes (in OpenSceneGraph with OpenGL). Among other things the user should be able to click on an scene object on the screen to move towards it.
The navigation technique should be integrated into another project which uses a vertex shader to apply a global deformation to the scene geometry. And here is the problem: Since the geometry is deformed using a vertex shader, it is not straight forward to un-project the mouse cursor position to the world coordinates of the spot the user actually selected. But I need those coordinates to perform the proper camera movement in my navigation technique.
One way of performing this un-projection would be to modify the vertex shader (used for the deformation) to let it also store the vertex' original position and normal in separate textures. Afterwards one could read those textures at the mouse position to get the desired values.
Now, as I said, the vertex shader belongs to another project which I actually don't want to touch. One goal of my navigation technique is to be as generic as possible to be easily integrated into other projects as well.
So here is the question: Is there any feature in OpenSceneGraph or OpenGL that I did not consider so far? Anything that allows me to get the world coordinates of a fragment, independently of the vertex shader coder?
Well, you could always do an OpenGL selection operation:
http://www.glprogramming.com/red/chapter13.html
Alternately, you could rasterize to a very small (1px*1px) framebuffer where the user clicked, read back the z-buffer and unproject the Z value you got into world space.
I'm having a problem getting accurate primitive colours when I'm using multi-texturing elsewhere in the scene. Basically, I have some lines and polygons that I am trying render over a video texture (I'm using 3 stage multitexturing to create the video texture)... Anyhow, I know the problem is not alpha related... In fact, I know that in my texture update function if I just comment out the calls to glBindTexture() for texture levels 1 and 2, the primitive color is fine (so leaving texture level 0)... Is it trying to multitexture the primitives too (even though I'm obviously not setting texture coordinates for primitives)?
Make sure to disable multitexturing when not using it. OpenGL uses a state machine, so if you turn on a texture it will stay on until you explicitly turn it off.
Just because you're not setting coordinates, doesn't mean OpenGL will assume you're not using the texture.