Active Oldest Votes. Like the following: Where , is the position of the first vertex in pixels and 0,0 is the UV coordinate. Improve this answer. Luke B. Wikipedia says that you can also calculate the coordinates. Or do I just manually assign the UV values? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete?
Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. Now live: A fully responsive profile. Beyond these, three. The Texture class is a wrapper around an HTML image element with some extra settings related to being used as a texture instead of a normal image. We can access the original image under image. Examples of the settings available through the texture class are. We can also specify various filtering using.
In other words, these settings control what algorithm is used to zoom in or out on the image. There are also several properties like.
Two other important settings are. Take a few minutes to explore the documentation page and check out the options available when working with textures. There are many ways of preparing images for use as textures, but the easiest is to take a photograph of an object. We can improve this by creating by using the original image to create additional textures for other material properties like bumps or roughness. Check out this set of textures on freepbr. For surfaces like these, an artist has to flatten out the photo and connect each point in the flattened image to a corresponding point on the 3D model, again using UV mapping.
This is typically done in an external modeling program, not in three. For common surfaces like brick walls and wooden floors, you can find high-quality texture sets like the one above around the web, many of them for free. The individual pixels that make up an image represent color.
Another way of looking at this is that an image is a 2D array of colors. This data can represent anything. Although technically incorrect, a texture is also often referred to as a map , or even a texture map , although map is most commonly used when assigning a texture to a material. Below, we show you how to assign the uv-test-bw. A digital image is a 2D array of pixels, each of which is a tiny dot that contains a single color. Our screen is also made up of a 2D array of tiny dots, each of which displays a single color, and we call these pixels too.
However, the pixels that make up a screen are actual physical objects, LEDs or OLEDs or some other high-tech device, while the pixels that make up an image are just numbers stored in a file. UV mapping is a method for taking a 2-dimensional texture and mapping it onto a 3-dimensional geometry.
This is where the name UV mapping comes from. If one dimension shrinks to a single pixel, it is not reduced further, but the other dimension will continue to be cut in half until it too reaches one pixel. In any case, the final mipmap consists of a single pixel. Here are the first few images in the set of mipmaps for a brick texture:. You'll notice that the mipmaps become small very quickly. The total memory used by a set of mipmaps is only about one-third more than the memory used for the original texture, so the additional memory requirement is not a big issue when using mipmaps.
Mipmaps are used only for minification filtering. They are essentially a way of pre-computing the bulk of the averaging that is required when shrinking a texture to fit a surface. To texture a pixel, OpenGL can first select the mipmap whose texels most closely match the size of the pixel. It can then do linear filtering on that mipmap to compute a color, and it will have to average at most a few texels in order to do so. In OpenGL 1. However, my sample programs do not use mipmaps.
OpenGL can actually use one-dimensional and three-dimensional textures, as well as two-dimensional. Because of this, many OpenGL functions dealing with textures take a texture target as a parameter, to tell whether the function should be applied to one, two, or three dimensional textures. There are a number of options that apply to textures, to control the details of how textures are applied to surfaces.
Some of the options can be set using the glTexParameteri function, including two that have to do with filtering. OpenGL supports several different filtering techniques for minification and magnification. The filters can be set using glTexParameteri :. The values of magFilter and minFilter are constants that specify the filtering algorithm. The default MIN filter requires mipmaps, and if mipmaps are not available, then the texture is considered to be improperly formed, and OpenGL ignores it!
Remember that if you don't create mipmaps and if you don't change the minification filter, then your texture will simply be ignored by OpenGL. There is another pair of texture parameters to control how texture coordinates outside the range 0 to 1 are treated. As mentioned above, the default is to repeat the texture.
The alternative is to "clamp" the texture. This means that when texture coordinates outside the range 0 to 1 are specified, those values are forced into that range: Values less than 0 are replaced by 0, and values greater than 1 are replaced by 1.
Values can be clamped separately in the s and t directions using. When clamping is in effect, texture coordinates outside the range 0 to 1 return the same color as a texel that lies along the outer edge of the image. Here is what the effect looks like on two textured squares:. The original image lies in the center of the square. For the square on the left, the texture is repeated.
On the right, the texture is clamped. When a texture is applied to a primitive, the texture coordinates for a vertex determine which point in the texture is mapped to that vertex. Texture images are 2D, but OpenGL also supports one-dimensional textures and three-dimensional textures.
This means that texture coordinates cannot be restricted to two coordinates. In fact, a set of texture coordinates in OpenGL is represented internally in the form of homogeneous coordinates , which are referred to as s , t , r , q. Since texture coordinates are no different from vertex coordinates, they can be transformed in exactly the same way. OpenGL maintains a texture transformation as part of its state, along with the modelview and projection transformations.
The current value of each of the three transformations is stored as a matrix. When a texture is applied to an object, the texture coordinates that were specified for its vertices are transformed by the texture matrix. The transformed texture coordinates are then used to pick out a point in the texture.
Of course, the default texture transform is the identity transform , which doesn't change the coordinates. The texture matrix can represent scaling, rotation, translation and combinations of these basic transforms.
For example to install a texture transform that scales texture coordinates by a factor of two in each direction, you could say:.
Since the image lies in the st -plane, only the first two parameters of glScalef matter. For rotations, you would use 0,0,1 as the axis of rotation, which will rotate the image within the st -plane. Now, what does this actually mean for the appearance of the texture on a surface?
In the example, the scaling transform multiplies each texture coordinate by 2. For example, if a vertex was assigned 2D texture coordinates 0. The texture coordinates vary twice as fast on the surface as they would without the scaling transform. A region on the surface that would map to a 1-by-1 square in the texture image without the transform will instead map to a 2-by-2 square in the image—so that a larger piece of the image will be seen inside the region.
In other words, the texture image will be shrunk by a factor of two on the surface! More generally, the effect of a texture transformation on the appearance of the texture is the inverse of its effect on the texture coordinates. This is exactly analogous to the inverse relationship between a viewing transformation and a modeling transformation.
If the texture transform is translation to the right, then the texture moves to the left on the surface. If the texture transform is a counterclockwise rotation, then the texture rotates clockwise on the surface. I mention texture transforms here mostly to show how OpenGL can use transformations in another context. But it is sometimes useful to transform a texture to make it fit better on a surface. And for an unusual effect, you might even animate the texture transform to make the texture image move on the surface.
Here is a demo that lets you experiment with texture transforms and see the effect. A box outlines the region in the texture that maps to a region on the 3D object with texture coordinates in the range 0 to 1. You can drag the sliders to apply texture transforms to see how the transforms affect the box and how they affect the texture on the object. See the help text in the demo for more information.
It's about time that we looked at the process of getting an image into OpenGL so that it can be used as a texture. Usually, the image starts out in a file.
OpenGL does not have functions for loading images from a file. As the name would imply, the most obvious use for a texture map is to add color or texture to the surface of a model. This could be as simple as applying a wood grain texture to a table surface, or as complex as a color map for an entire game character including armor and accessories.
However, the term texture map , as it's often used is a bit of a misnomer — surface maps play a huge role in computer graphics beyond just color and texture.
In a production setting, a character or environment's color map is usually just one of three maps that will be used for almost every single 3D model. Specular maps also known as gloss maps. A specular map tells the software which parts of a model should be shiny or glossy, and also the magnitude of the glossiness.
Specular maps are named for the fact that shiny surfaces, like metals, ceramics, and some plastics show a strong specular highlight a direct reflection from a strong light source.
If you're unsure about specular highlights, look for the white reflection on the rim of your coffee mug. Another common example of specular reflection is the tiny white glimmer in someone's eye, just above the pupil. A specular map is typically a greyscale image and is absolutely essential for surfaces that aren't uniformly glossy.
An armored vehicle, for example, requires a specular map in order for scratches, dents, and imperfections in the armor to come across convincingly.
Similarly, a game character made of multiple materials would need a specular map to convey the different levels of glossiness between the character's skin, metal belt buckle, and clothing material. A bit more complex than either of the two previous examples, bump maps are a type of texture map that can help give a more realistic indication of bumps or depressions on the surface of a model.
Consider a brick wall: An image of a brick wall could be mapped to a flat polygon plane and called finished, but chances are it wouldn't look very convincing in a final render.
0コメント