Opengl thick lines

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Opengl thick lines

I am a computer graphics researcher at Yale Univerisity. I enjoy language learning, visiting new places and occasionally do rock climbing. This tutorial is more expanded version of an answer on my stackoverflow question.

2D path extrusion and contour detection ("thick lines ")

To summarize the goal, we want to be able to draw lines in 3D that satisfy the next conditions:. The default OpenGL drawing of line strip geometry does not allow to render smooth non-broken lines, as well as to render them of customary thicker than default width:. One of the ways to solve the problem is to represent each line segment as a set of triangles.

Adjacent triangles or quads are drawn without any gaps between them. In this case we have to deal with two problems:. To address the problem 1, we have to make sure the geometry is always facing the camera, i. For the problem 2, the solution is similar - re-adjust the ribbon width with the change of viewport. A very effective way to achieve the desired effect is to use GLSL shaders. Assuming the familiarity of the aforementioned programs, we will move directly to the implementation details.

The presented code is heavily based on the Cinder library discussion threadand the main principle of triangle coordinates calculation is taken from there as well.

The vertex shader is what helps to transform the 3D world coordinates into screen coordinates. Simply speaking, this is where we deal with lines being always faced towards the camera. In order to implement it, we have to use model-view-projection MVP matrix which is the matrix that is updated on every view change. The position of each vertex of the triangle is calculated in relation towards the viewport of the widget which displays the whole scene.

This allows the lines to have a constant thickness in spite of the their location in 3D world. Refer to the source code for more details on shader implementation. The fragment shader is a simple pass-through shader. It takes the incoming color and assigns it to each fragment:.

For debugging purposes, I set up the color in the shader to green, so that to verify all the previous steps of shader program has completed successfully.

We need to provide two uniform s: for MVP matrix and the Viewport. When using OSG, the best way to do it is by using callbacks. In this case we need to derive from osg::Uniform::Callback.

Below are the code snippets for each of the callbacks:. Of course, we need to pass the pointer on a camera that is attached to the viewer that displays the scene. In a similar way we define the callback for viewport:. By following the OSG tutorials on how to set up and use shaders withing an OSG program, we create an osg::Program instance and attach to it the created shaders. This is how it can be done in OpenSceneGraph:.

After we need to add the necessary uniforms, including the MVP matrix and viewport. And finally connect the shader program to the state set of the geometry. Note: in order to avoid an aliased look of the shadered lines, we have to enable multi-sampling. Some screenshots of the result lines. Note how the connection between the anchor point does not look broken compared to the red line. For this case we turned on the multi-sampling. The demonstration of ability to produce much thicker lines.I need a way to render lines for the new renderer I mentioned in a previous post.

Instead I decided to write my own implementation of that feature. The easiest way I came up with was by using geometry shader.

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Basically geometry shader gets line segments as input and then outputs a triangle strip quad for each of them. The result looks something like this:. If you think about it then it makes perfect sense. Each line segment has different direction, thus the outer edges will not be continuous. Instead of the lhs vector being perpendicular to the line segment it should be the bisector of the corner formed by adjacent line segments. That bisector vector is where the outer edges of 2 line segments meet up.

Thus that vector is shared between beginning of one line segment and end of another one. An easy way to get the bisector would be to take unit length line segment or their extension vectors and then lerp to the middle point. All the geometry shader knows about right now is the current line segment. Thus we need to use OpenGL 3. Good programmer as you are, you will immediately notice that it would cause a buffer underflow at index 0 and a buffer overflow at index n This means that we will be missing the first and the last line segment.

There is 2 ways I can think of to get around it. First you could duplicate the last and first indices in your index buffer. The first option would require a special case in geometry shader and editing the index buffer.

The second one would require editing both index and vertex buffer but no special case in the shader. For example line loops - with those extra 2 vertices you could make sure that the ends line up properly. I still went with the first one for now.

First how to make the line width constant. To solve that we divide the bisector vector by the dot product between itself and the lhs calculated from direction vector that is perpendicular to current line semgent.

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This will scale the bisector vector larger based on the angle. Another thing we need to do is to keep the lhs vector always on the same side of the line segment.

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We take the dot product between the bisector vector and the lhs vector calculated from direction. If the dot product is negative, we flip it.These were both super-useful features for writing 3D editing software, and my program is worse in OpenGL 4 for their loss.

It would be extremely difficult to reproduce the stipple appearance in a shader, and thick lines are better for more highly visible editor guides. Could you do a little research or at least ask a question on another section of the forum before deciding to post a suggestion? Line width other than 1.

I doubt that modern hardware has any dedicated functionality for that. And you can do it as well, you can also use GS. OpenGL is not a graphics library to provide you with bells and whistles. It is an API, that maps to hardware functionality. All those extra features you should implement yourself with provided rendering and computation functionality or, alternatively, use 3rd-party libraries which do it already.

Nvidia0. As long as you stay within the line width range of the driver, you can use wide lines. The implementation may still emulate wide lines and report back capabilities based on the emulation, and this would be prefectly legal so long as it remained conformant e.

The days of OpenGL specifying idealized functionality which hardware must then emulate in software are over, thankfully. Line stipple and line thickness OpenGL. Nowhere March 17,pm 2.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Game Development Stack Exchange is a question and answer site for professional and independent game developers. It only takes a minute to sign up.

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I have a list of points 3D and want to draw a line connecting all points with a specified width. The real challenge of this task is to make the line look "pleasant" for the user; meaning the joints should be round. I'm not sure you should go through the burden of using a library just for rounded joints. You could draw thick lines with discs at the intersections, i.

In the CAD world a rounded corner like you describe is called a Fillet while a hard angled transition is called a Chamfer. Since you are dealing with lines, which is a CAD specialty, see if anything here: Discussion on CAD libraries has something you can use.

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Home Questions Tags Users Unanswered. Render a polyline with rounded joints Ask Question. Asked 7 years, 11 months ago. Active 7 years, 11 months ago.

opengl thick lines

Viewed 3k times. It should be similar to this: Is there any library which brings this functionality?

opengl thick lines

Laurent Couvidou 8, 2 2 gold badges 35 35 silver badges 54 54 bronze badges. Andreas Roth Andreas Roth 1 1 silver badge 4 4 bronze badges. Look into bezier curves. My unserstanding is that you're only interested in rounded joints, like this: vaserenderer. Am I right?

opengl thick lines

Active Oldest Votes. Laurent Couvidou Laurent Couvidou 8, 2 2 gold badges 35 35 silver badges 54 54 bronze badges. Note that since the user is talking about line drawing in 3d, the 'thick lines' should actually be cylinders and the discs should be spheres since they could be being looked at from any angle; if users will be inspecting the lines up close then you'll have to be a little bit careful about polygonalizing your shapes especially your sphere to avoid cracks where the cylinders merge into the sphere.

Patrick Hughes Patrick Hughes Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.Sorry if the question seems to be too simple for the advanced coding forum, but I guess to get nice lines it needs advanced knowledge.

In 2D, perpendicular is simple. In 3D, you need more information. If you want your thick line to lie flat on the ground, find the displacement vector such that it is most perpendicular to the line segment and the up vector. So far, this only handles the case of one thick line segment 4 pts.

Given two lines coming together at an angle, you have some options for how to handle the corner:. You can use two pairs of points, one for the end of segment A and set for the the start of segment B and let the tristrip rendering span the gap. This looks best, but adds many more points than the original line. Antialiasing is normal polygonal edge antialiasing in this case.

My website has some 2 years old screenshots of what it gives when you add some textures. Many thanks for replies, folks! How do you draw nice thick lines? OpenGL: Advanced Coding. Cyranose March 17,pm 2. Hope that helps.

opengl thick lines

NiCo1 March 17,pm 3. SeskaPeel March 17,pm 4. SeskaPeel March 17,pm 5.I join an image. What is the cause that thick lines? How to disable that?

Yes but there is a so big difference between thin and thick lines… The 3D view looks like a cartoon with big edges. Enabling the blending does not change anything. For me it seems unusable like this…. Your line coordinates are most likely bad between pixels instead of at center of pixels. However, i guess something else is also going on as the partially covered pixels look full color and not a mix between line and scene colors blending not enabled?

I checked. Your line has a thickness of 1 pixel. When you enable smoothing, thickness becomes 3. So it is normal. Yes the blending is disable on my screenshot. And I think I used the classical code :. Will this method generate more thin lines or will I only have better performances? With FSAA, the lines would look fine.

Try them and see which one you like. You can just go into control panel and enable it. IMO, 6x and above yields good results.

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If you like it, then you can create a FSAA context programmatically. To draw lines that appear thinner than 1px, scale the alpha, e. Perfectly vertical or horizontal lines with glLineWidth 1 wide may seem thinner than diagonal lines. It may be more efficient memory wise smaller framebuffer footprint. Also take note that some Intel hardware has absolutely p! Remdul, I tested again after your post but no : I can not obtain good results.

And blending works but gives artifacts in some cases in 3D view. If you say that it may work then there are errors in our code but I can not find where…. So I did a test in my code using a Nehe tutorial.

I join the result. It is ok for me and I have no more artifacts in 3D. OpenGL: Basic Coding. AllForum March 17,am 1. AllForum March 17,pm 3. Thanks for your answer.

For me it seems unusable like this… Do you confirm that it is the correct behavior? From hardware point of view. It also depends on the card that you use.Copy code. Please tell us why you want to mark the subject as inappropriate. Maximum characters. Report Inappropriate Cancel. From : guest. Content :. Type the characters you see in the picture below.

How to draw thick and smooth 3D lines in OpenSceneGraph / OpenGL

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