Add a comment. Active Oldest Votes. So, the projection matrix I'm sure you've seen images like this: This allows you to define your arbitrary 3D coordinate system. The default projection or "viewing volume" is an orthographic -1 to one cube. Improve this answer. Thanks a lot!!!! I understood the problem wasn't at DrawImage but at some mouse x, y coordinates detection I did :P — user Reto Koradi Reto Koradi The Overflow Blog.
Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Visit chat. So depending on the OS you are using, you may have to include two or three potential paths for the OpenGL header files, and use ifdef to turn off the include files that don't exist.
These two functions are the most important in any OpenGL program. Both of these functions are written by the programmer. They also need to make sure these functions run as fast as possible, because they will be called several times per second and if they run too slowly, users will notice lag in the program.
Where w and h are aliases typedef's of int, so you can treat these as integers and use them anywhere where an int is accepted. Below is a sample resize function.
It resizes the viewport to the window size whenever it changes. In this case we switch to the projection matrix, which is where all of the coordinates for our drawings are stored. We are going to resize this matrix to ,, This function clears it to the identity matrix, which is equivalent to no transformation at all. One consequence of this is that all shapes have to be drawn within this range to be visible. This is then scaled to the viewport size after applying the modelview matrix to the projection transformation.
The fragment shader depends on attributes like the color and texture coordinates, which will usually be passed from input to output without any calculations.
Remember that our vertex position is already specified as device coordinates and no other attributes exist, so the vertex shader will be fairly bare bones. The version preprocessor directive is used to indicate that the code that follows is GLSL 1.
Next, we specify that there is only one attribute, the position. The type of the values within these constructs is always a float. Since the position attribute consists of only an X and Y coordinate, vec2 is perfect. You can be quite creative when working with these vertex types.
In the example above a shortcut was used to set the first two components of the vec4 to those of vec2. These two lines are equal:. When you're working with colors, you can also access the individual components with r , g , b and a instead of x , y , z and w.
This makes no difference and can help with clarity. For these to function correctly, the last value w needs to have a value of 1. Other than that, you're free to do anything you want with the attributes and we'll see how to output those when we add color to the triangle later in this chapter. The output from the vertex shader is interpolated over all the pixels on the screen covered by a primitive. These pixels are called fragments and this is what the fragment shader operates on.
Just like the vertex shader it has one mandatory output, the final color of a fragment. It's up to you to write the code for computing this color from vertex colors, texture coordinates and any other data coming from the vertex shader.
Our triangle only consists of white pixels, so the fragment shader simply outputs that color every time:. This is because a fragment shader can in fact output multiple colors and we'll see how to handle this when actually loading these shaders. The outColor variable uses the type vec4 , because each color consists of a red, green, blue and alpha component.
Colors in OpenGL are generally represented as floating point numbers between 0. Compiling shaders is easy once you have loaded the source code either from file or as a hard-coded string.
Just like vertex buffers, creating a shader itself starts with creating a shader object and loading data into it. Unlike VBOs, you can simply pass a reference to shader functions instead of making it active or anything like that. The glShaderSource function can take multiple source strings in an array, but you'll usually have your source code in one char array. The last parameter can contain an array of source code string lengths, passing NULL simply makes it stop at the null terminator.
Be aware that if the shader fails to compile, e. See the block below for info on how to debug shaders. Retrieving the compile log. The log may also report useful warnings even when compiling was successful, so it's useful to check it out from time to time when you develop your shaders. Again, be sure to check if your shader was compiled successfully, because it will save you from a headache later on.
Up until now the vertex and fragment shaders have been two separate objects. While they've been programmed to work together, they aren't actually connected yet. This connection is made by creating a program out of these two shaders.
Since a fragment shader is allowed to write to multiple framebuffers, you need to explicitly specify which output is written to which framebuffer.
This needs to happen before linking the program. However, since this is 0 by default and there's only one output right now, the following line of code is not necessary:. Use glDrawBuffers when rendering to multiple framebuffers, because only the first output will be enabled by default. After attaching both the fragment and vertex shaders, the connection is made by linking the program. It is allowed to make changes to the shaders after they've been added to a program or multiple programs!
It is also possible to attach multiple shaders for the same stage e. A shader object can be deleted with glDeleteShader , but it will not actually be removed before it has been detached from all programs with glDetachShader.
Although we have our vertex data and shaders now, OpenGL still doesn't know how the attributes are formatted and ordered. You first need to retrieve a reference to the position input in the vertex shader:.
The location is a number depending on the order of the input definitions. The first and only input position in this example will always have location 0.
There is always a higher chance that a GL driver implements rasterization correctly than smooth- line drawing. As far as I know, most hardware support sub- pixel accuracy rasterization. It would probably work. In my testing, there are often rounding errors which cause tiny artifacts. That is not perfect, but still good. Again I cannot guarantee, the best way is to test it yourself. Using triangles to approximate line segments is not a new thing, and I believe many programmers did that back from OpenGL 1.
The important thing is calibrating the code to give such high quality and publishing it. Drawing good looking lines should be a basic feature of a graphics API. It is strange after all these years we do not have an elegant solution and many programs just tolerate aliasing.
The code is designed for easy integration and to replace "traditional" line drawings with ease. So download the zip file and include the header to test it out.
If you find this useful, I just hope you cite this page. The fade polygon technique is extended to achieve anti- aliasing for shapes more complex than a line segment: polylines.
Do not miss the second episode, Drawing polylines by tessellation, of this article. NET V is released!
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