So i went toying around with my old sixaxis gamepad on my pc and decided to add gamepad support to one of my apps, turns out it’s not that hard so i thought i would add a quick tutorial about it.
First of all it’s worth noting that a gamepad and a joystick is the same thing from a technical perspective. secondly the specific setup is using windows own built in joystick interface which means that we are limited to 6 analog axis and 32 buttons, which is plenty as the classic playstation dualshock controller (which almost every other controller is based on in some way) only has 4 analog axis and 17 buttons (gyros and accelerometers does not count as we can’t use them). Read more »
Transform feedback, is one of the tools of the trade not often discussed on the net, in fact i couldn’t find a single tutorial, so i better write one. the essential function of this little feature is to enable you to do very complicated stuff in the geometry shader, stuff that would inevitably make things run slowly, or to assemble a vbo using tiny little parts and then save it to a buffer for later use, or for that matter constant use. Read more »
In this part we will be doing a bit of simple geometry instancing with a minecraft twist, basically what we are going to do is first generate a volumetric landscape of sorts, then render it using cubes, but not the usual way, we are going to do it as a particle system, which is i guess a little bit more than usual as it involves other stuff than strictly openGL, and since there are a few things i want to try out in this field you will be seeing more of it.
This tutorial assumes that you have all the stuff needed for part 1 and in addition texturing available. Read more »
New in OpenGL 3.2 is so called geometry shaders, if you don’t know what they are then what the essentially do is allow you to create new or duplicate geometry. Like instead of drawing a bunch of cubes one after another you could just render a point cloud and let the geometry shader “upgrade” them to cubes, which is probably how i would render minecraft if i where it’s creator, which i would if i had a hat half as awesome as notch does.
Read more »
Hi, here is a little Yule gift for all you GL junkies out there, it’s a short quick and easy tool for taking a screen shot into the tga format, sure it’s uncompressed and doesn’t increment the file name, but it’s pretty slick.
void screenshot (char filename[160],int x, int y)
{
// get the image data
long imageSize = x * y * 3;
unsigned char *data = new unsigned char[imageSize];
glReadPixels(0,0,x,y, GL_BGR,GL_UNSIGNED_BYTE,data);
// split x and y sizes into bytes
int xa= x % 256;
int xb= (x-xa)/256;
int ya= y % 256;
int yb= (y-ya)/256;
//assemble the header
unsigned char header[18]={0,0,2,0,0,0,0,0,0,0,0,0,(char)xa,(char)xb,(char)ya,(char)yb,24,0};
// write header and data to file
fstream File(filename, ios::out | ios::binary);
File.write (reinterpret_cast(header), sizeof (char)*18);
File.write (reinterpret_cast(data), sizeof (char)*imageSize);
File.close();
delete[] data;
data=NULL;
}
|
Usage: screenshot (“test.tga”,800,600);
Just call the function with the correct window size just before SwapBuffers and it will take a screen shot of everything in the frame buffer, easy.
In our third installment we are looking into replacing all the matrix math previously built into openGL, what I am going to show you replaces most of it almost exactly like openGL used to work, naturally if your doing something a bit more advanced like a game or so, I would suggest that you use your scene graph to generate new matrices.
It’s really quite simple though, and as with the previous part we have to do some changes a bit here and there, so I am going to start with the most generalized bit and work my way down, and finally end up with the classic rotating cube.
But first the prerequisites, I am assuming that you started where part 2 left off, we will also need the following functions made to work
glGetUniformLocation
glUniformMatrix4fv
Step 1 – the shader
it’s really not that much but after
add
this will be where we send our new matrix to.
Then later in the code you need to do something like this to use our matrix
You could use and I almost recommend that you use two matrices one for the camera and one for the model transformation, but I leave that task to you.
Please note that the order of the multiplication is important. Read more »
In this part I will show you what you must do to render even the smallest speck of graphical garbage on the screen in the openGL 3.0 API, it’s somewhat simple once you have all the tools.
First you need a good GLSL shader implementation because nothing will render without it, you can use mine if you want but just remember that we are gonna modify it a bit so it can’t be to abstracted.
Next you need to take a look at the VAO tutorial since well be using that too, naturally since we are using VAO well also be using VBO and in this example I have 3 buffers with the vertex, texture and normal coordinates for a cube, you could use anything, but I am using a cube.
We are also going to use 4 new functions so go ahead am make them work as well.
glVertexAttribPointer
glBindAttribLocation
glDisableVertexAttribArray
glEnableVertexAttribArray
Finally remove anything that has to do with matrices, well discuss those in part 3, in fact remove or comment out any deprecated function (you can find them in part 1).
Now then, there are about four steps to this, that is there are 4 things you need to change in your already existing code for things to work, so I will explain them in order. Read more »
Welcome to a series I have planned on OpenGL 3.0 regarding the forward compatible mode, or in layman’s terms, using OpenGLwithout all the stuff that got cut.
It’s quite a different beast to work with, even I have problems getting my head around it since so much things that you used for every other line has to be done differently, I find myself adding the line glTranslatef(…. only to suddenly stop thinking “o, right, doesn’t work anymore”.
It’s a bit harder also as you have to use shaders or it won’t be drawn, you cant just use a VBO like before but instead you have to bind it to a input variable.
In short everything is different, but I will try to guide you trough the basic stuff, but look at it from the bright side, now you have no more excuse not to code the way it should be done.
So what got cut well quite a bit, take a look at http://www.opengl.org/documentation/specs/ and download the 3.0 specification and then check under the section called “The Deprecation Model”, but here are some highlights Read more »
With openGL 3 came a few cool features most of these are pretty small and quick to learn, VAOs are among these, I really didn’t want to write a full fledged tutorial about it before, but seeing as I’m changing the format to promote shorter and more article like posts, it seemed like as good as place as any to start.
There hasn’t been that much written about the vertex_array_object extension, also there is some confusion on where to use it and how.
Simply put it couldn’t be simpler, it’s used to make the daily life of using VBOs easier and the code prettier, earlier you had to call these three functions for each buffer to set up rendering, normally that would be at least 3.
glEnableClientState
glBindBuffer
glTexCoordPointer Read more »
In the last previous tutorial we explored the depth shadow maps in all it’s aliasing glory.
I showed you ho to fix the steep angle artifacts by using the diffuse term, and the shadow poping by adding a bias to the shadows.
In this lesson we are going to implement something called Percentage Closer Filtering or PCF as it is more commonly called, the name doesn’t exactly reveal what it does.
It is in fact a way to multi sample the shadows and this is pretty simple, so simple that i am not going to supply you with anything other than the new shader file, the rest is exactly the same as tutorial 03a.
1. transform the texture coordinates first two values by a really small amount.
2.make a shadow test against those coordinates.
3. repeat 1 and 2 as many times as needed..
4. take the collective result from the shadow tests and divide it with the number if samples you just did.
Lets demonstrate this with some code.
First we set up some variables + load the other textures besides the shadows.
Since we are also going to do 25 samples we want to eliminate as much as possible from the loop, that is why i added the inverted bias to gl_TexCoord[2].z instead of the shadow value.
float blur_spread[5];blur_spread[0] = -0.003;
blur_spread[1] = -0.001;
blur_spread[2] = 0.000;
blur_spread[3] = 0.001;
blur_spread[4] = 0.003;
float samples=1.0/25.0;
gl_TexCoord[2] = gl_TexCoord[2]/gl_TexCoord[2].w;
gl_TexCoord[2]=(gl_TexCoord[2]+ 1.0) * 0.5;
gl_TexCoord[2].z -=0.005;
vec4 base = texture2D(texunit0, gl_TexCoord[0].xy);
vec3 norm = texture2D(texunit1, gl_TexCoord[0].xy).xyz*2.0-1.0;
float shade=0.0;
float shadow=0.0;
int x=0;
int y=0; |
next do the sampling, note that because a division is more problematic than a add, we pre divided the samples so instead of adding one for each sample we are adding 0.04, this saves us the trouble of having to divide at runtime.
for(x=0;x<5;x++)
{
for(y=0;y<5;y++)
{
shadow = texture2D(texunit2,gl_TexCoord[2].xy+vec2(blur_spread[x],blur_spread[y]));if(shadow > gl_TexCoord[2].z)
shade+=samples;
}
} |
Great now all we have to do is include the rest and we are done
norm = normalize(gl_NormalMatrix * norm);
float fresnel =max((norm.z-0.6)*-1.0,0.0);
float diffuse = max(dot(lightVec, norm),0.0);
float specular = max(dot(reflect(lightVec,norm), viewVec), 0.0)*1.7;
specular=pow(specular,8.0);
shade*=diffuse;gl_FragColor = (base* shade)+(vec4(0.0,0.1,0.3,0.0)*fresnel)+
(vec4(0.5,0.5,0.4,0.0)*specular*shade); |
You can now begin to play around with the numbers, increasing the values in blur_spread will make it a bit more blurry, but then other artifacts show up, these can be fixed by fiddling with the bias parameters, but ultimately PCF is just a hack and won’t work every time.
I originally planned to include a version that changed the blurriness according to the distance from the shadow casting surface, it looked pretty good, unfortunately not good enough in all situations, it was done by getting the distance between the fragment and the shadow map depth value and with this manipulating the values in blur_spread.
It would have worked if it whereat for those meddling kids(read:artifacts).
Test and see if you can do it.
Download the new shader file for this tutorial, to get the rest download the previous tutorial
Games, Tutorials | Peter Wallström | 
March 15, 2012 16:24 | 
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