Opengl sphere texture mapping example

Let's assume you want to create something that looks like the planet earth. You want to apply a map of the earth to a sphere. There are 2 ways to texture a sphere. Either by applying a cubemap or by applying a 2D texture.

For best result, use a cubemap. The problem with applying a 2D texture is that when you wrap a 2D texture onto a sphere, the top and bottom area of the sphere, the texture looks squeezed. Load a cubemap as shown in Creating a Cubemap Texture Let's assume that we'll be using shaders.

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If you haven't learned shaders yet, now is the time. This code is in GLSL 1. The fragment shader. Notice that the normal has been copied to TexCoord0 and this will be used to sample the cubemap. Either you need to write your own code to create a sphere and you compute the texcoords yourself or you use another library like GLU or glhlib. From OpenGL Wiki.

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opengl sphere texture mapping example

This page was last edited on 20 Octoberat The definition of sphere is a 3D closed surface where every point on the sphere is same distance radius from a given point. The equation of a sphere at the origin is. Since we cannot draw all the points on a sphere, we only sample a limited amount of points by dividing the sphere by sectors longitude and stacks latitude. Then connect these sampled points together to form surfaces of the sphere.

The range of sector angles is from 0 to degrees, and the stack angles are from 90 top to degrees bottom. The sector and stack angle for each step can be calculated by the following.

It also creates other vertex attributes; surface normals and texture coordinates. In order to draw the surface of a sphere in OpenGL, you must triangulate adjacent vertices to form polygons. It is possible to use a single triangle strip to render the whole sphere. However, if the shared vertices have different normals or texture coordinates, then a single triangle strip cannot be used. Each sector in a stack requires 2 triangles.

But, the top and bottom stacks require only one triangle per sector. The code snippet to generate all triangles of a sphere may look like. Download: sphere. This example constructs spheres with 36 sectors and 18 stacks, but with different shadings; flat, smooth or textured.

Texturing a Sphere

Or, download sphereShader. This problem can be solved using Icosphere or Cubesphere. Another way to create a spherical geometry is subdividing an icosahedron multiple times. Icosahedron is a regular polyhedron with 12 vertices and 20 equilateral triangles the first left image below. Each triangle of an icosahedron is divided into 4 equal sub-triangles per subdivision.

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Please see the following orthogonal projection images of icosahedron. A typical point at latitude Note that is the elevation height of the point and is the length of the projected line segment on XY plane. The subdivision algorithm is splitting the 3 edge lines of each triangle in half, then extruding the new middle point outward, so its length the distance from the center is the same as sphere's radius.

In order to generate a texture map of an icosphere, you need to unwrap the 3D geometry on a plane paper model. I use the following texture coordinates of vertices instead of normalized coordinates from 0 to 1, so the coordinate of each vertex can be snapped to an exact pixel on the image.

For example, if a texture size is x, then the horizontal step is pixels and the vertical step is pixels.David Bernstein James Madison University. Steps in the Initialization Process. Name the texture Bind the texture to its name Specify the parameters to use Specify an application mode either replace or modulate Create the texture object Enable texture mapping. Steps in the Rendering Process.

Select a texture Specify a mapping from the texture to pixels. Naming a Texture. Naming a Texture cont. Binding a Texture to a Name. Binding a Texture to a Name cont. Specifying Parameters.

GLSL Programming/GLUT/Textured Spheres

Specifying Parameters cont. Specifying the Application Mode.

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Specifying the Application Mode cont. Creating the Texture Object. Creating the Texture Object cont. Enabling Texture Mapping. Enabling Texture Mapping cont. Rendering cont.

Sphere Mapping Quadrics In OpenGL

Reading Images. Reading Images cont. Using Multiple Textures. Using Multiple Textures cont. Manipulating Textures. Non-2D Textures. One-Dimensional: Essentially a 2D texture with a height of 1 Three-Dimensional: Different grids at different depths Mostly used for medical imaging.So far, every geometric primitive has been drawn as either a solid color or smoothly shaded between the colors at its vertices - that is, they've been drawn without texture mapping.

If you want to draw a large brick wall without texture mapping, for example, each brick must be drawn as a separate polygon. Without texturing, a large flat wall - which is really a single rectangle - might require thousands of individual bricks, and even then the bricks may appear too smooth and regular to be realistic. Texture mapping allows you to glue an image of a brick wall obtained, perhaps, by scanning in a photograph of a real wall to a polygon and to draw the entire wall as a single polygon.

Texture mapping ensures that all the right things happen as the polygon is transformed and rendered.

opengl sphere texture mapping example

For example, when the wall is viewed in perspective, the bricks may appear smaller as the wall gets farther from the viewpoint.

Other uses for texture mapping include depicting vegetation on large polygons representing the ground in flight simulation; wallpaper patterns; and textures that make polygons look like natural substances such as marble, wood, or cloth.

The possibilities are endless. Although it's most natural to think of applying textures to polygons, textures can be applied to all primitives - points, lines, polygons, bitmaps, and images. Because there are so many possibilities, texture mapping is a fairly large, complex subject, and you must make several programming choices when using it. For instance, you can map textures to surfaces made of a set of polygons or to curved surfaces, and you can repeat a texture in one or both directions to cover the surface.

A texture can even be one-dimensional. In addition, you can automatically map a texture onto an object in such a way that the texture indicates contours or other properties of the item being viewed.

Shiny objects can be textured so that they appear to be in the center of a room or other environment, reflecting the surroundings off their surfaces. Finally, a texture can be applied to a surface in different ways. It can be painted on directly like a decal placed on a surfaceused to modulate the color the surface would have been painted otherwise, or used to blend a texture color with the surface color.

If this is your first exposure to texture mapping, you might find that the discussion in this chapter moves fairly quickly. Textures are simply rectangular arrays of data - for example, color data, luminance data, or color and alpha data. The individual values in a texture array are often called texels. What makes texture mapping tricky is that a rectangular texture can be mapped to nonrectangular regions, and this must be done in a reasonable way.

Figure illustrates the texture-mapping process.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I am trying to add a texture to a sphere, it works, but I keep getting an error. Below is a picture of what I get. I don't know what this GL error: Invalid operation error is referring to. I think it has to do with my code. I'm not sure if I'm reading from my file correctly. I apologize if my code is confusing to read. Let me know if you see what is wrong with my code. I tried getting read of this error but it still shows up. Any ideas why? As the documentation of glBindTexture states "You must use glGenTextures to generate a set of new texture names.

That means you have to fill your "surface" variable with a valid texture name first. That is probably where your GL error comes from. Third, to figure out where what is causing the GL error on your own it's a good idea to create a macro that calls glGetError and prints a log message if there was an error.

opengl sphere texture mapping example

Than you can spread that macro between calls to the GL to narrow down where the error occured. The problem in this code was this line glEndList. Once I removed it the program worked without any errors. Learn more. Asked 7 years, 1 month ago. Active 5 years, 3 months ago. Viewed 12k times. Below is a picture of what I get, I don't know what this GL error: Invalid operation error is referring to. Here is the code I am using to draw this sphere. TRod TRod 1 1 gold badge 6 6 silver badges 18 18 bronze badges.

What object is that?In this tutorial, we start with a single texture map on a sphere. More specifically, we map an image of the Earth's surface onto a sphere. Based on this, further tutorials cover topics such as lighting of textured surfaces, transparent textures, multitexturing, gloss mapping, etc. The horizontal coordinate is officially called S and the vertical coordinate T. However, it is very common to refer to them as x and y.

In animation and modeling tools, texture coordinates are usually called U and V. In order to map the texture image to a mesh, every vertex of the mesh is given a pair of texture coordinates. Thus, every vertex is mapped to a point in the texture image. The texture coordinates of the vertices can then be interpolated for each point of any triangle between three vertices and thus every point of all triangles of the mesh can have a pair of interpolated texture coordinates.

These texture coordinates map each point of the mesh to a specific position in the texture map and therefore to the color at this position. Thus, rendering a texture-mapped mesh consists of two steps for all visible points: interpolation of texture coordinates and a look-up of the color of the texture image at the position specified by the interpolated texture coordinates. In OpenGL, any valid floating-point number is a valid texture coordinate.

To map the image of the Earth's surface onto a sphere, you first have to load the image. Since many techniques use texture mapping, it pays off very well to understand what is happening here. Therefore, let's review the shader code:. We'll need them in the fragment shader to convert them to texture coordinates in the space of the texture image.

The vertex shader then writes the texture coordinates of each vertex to the varying variable texCoords.

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For each fragment of a triangle i. In this case, we generate the texture coordinates algorithmically, but usually they are specified through your 3D modeler, and passed as additional vertex attributes. It is crucial that you gain a good idea of these steps in order to understand the more complicated texture mapping techniques presented in other tutorials.

In some 3D frameworks, you might have met parameters Tiling and Offseteach with an x and a y component. These parameters allow you to repeat the texture by shrinking the texture image in texture coordinate space and move the texture image on the surface by offsetting it in texture coordinate space. To reproduce this behavior, another uniform has to be defined:.

We can specify such a vec4 uniform for each texture.Sphere Environment Mapping is a quick way to add a reflection to a metallic or reflective object in your scene. Although it is not as accurate as real life or as a Cube Environment Map, it is a whole lot faster! We'll be using the code from lesson eighteen Quadrics for the base of this tutorial.

Also we're not using any of the same texture maps, we're going to use one sphere map, and one background image. Before we start The "red book" defines a Sphere map as a picture of the scene on a metal ball from infinite distance away and infinite focal point. Well that is impossible to do in real life. The best way I have found to create a good sphere map image without using a Fish eye lens is to use Adobe's Photoshop program.

First you will need a picture of the environment you want to map onto the sphere. Open the picture in Adobe Photoshop and select the entire image. Copy the image and create a new PSD Photoshop Format the new image should be the same size as the image we just copied.

Paste a copy of the image into the new window we've created. The reason we make a copy is so Photoshop can apply its filters. Instead of copying the image you can select mode from the drop down menu and choose RGB mode.

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All of the filters should then be available. Next we need to resize the image so that the image dimensions are a power of 2. Remember that in order to use an image as a texture the image needs to be x, x, etc. Under the image menu, select image size, uncheck the constraint proportions checkbox, and resize the image to a valid texture size. If your image is X90, it's better to make the image x than 64x Making the image smaller will lose alot of detail. The last thing we do is select the filter menu, select distort and apply a spherize modifier.

You should see that the center of the picture is blown up like a balloon, now in normal sphere maps the outer area will be blackened out, but it doesn't really matter. Save a copy of the image as a. BMP and you're ready to code!


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