Computer Graphics

Friday, April 12, 2013

Graphics Blogs To Date - Links

Week 10 - Intermediate Graphics

This is going to be my last blog for this class, and I just wanted to highlight my experiences learning about shader based OpenGL and special effects in games.

I have to say that when I started this course I expected it to be hard. I had looked at GLSL over the holidays and knew that what I had learned in the Introduction to Graphics course wasn't enough to get up to the level that we'd be working at.

During the first week we went through basic old deprecated OpenGL and how it works. This was a good summary of the Introduction to Graphics course, and was a good refresher after the holidays. During the second week we went over the shader pipeline, and learned what exactly vertex and fragment shaders. This was covered towards the end of the Intro to Graphics course but not very clearly, so this lecture made it very simple as to what exactly the vertex and fragment shaders do.

All the lectures after that were easy to follow along, even if I didn't understand the concepts at first.

My one problem, which was a problem for me really, was that in our Introduction to Graphics course, I didn't fully grasp how to use VAOs and VBOs. The reason this was a problem for me was that I really wanted to try some advanced shaders that required the use of core GLSL but I couldn't because my framework had been fully set up in archaic OpenGL. Hopefully over the summer I will be able to complete every shader we learned in class, as I understand the material at a high-level, but I just need to implement it to get experience with the shader effects and how they work.

The only thing that I would say I wished we could have had in this course was learning about color spaces and the real math behind color. We had one tutorial that mentioned the subject of color spaces, and we talked about, at a very high level, what HSL (hue, saturation, luminance) was and how we can use it to perform certain post-processing, but I wish we had covered it a little more in-depth or been given some good resources so that we could read up on the subject on our own time. I did do my own research however to figure out how to do some Photoshop post-processing replication in shaders, but I felt like I wasn't even scratching the surface.

Which leads me to the aspect of this course that I love, which is the fact that we have to teach ourselves. I hate information being spoon-fed to me. I always end up zoning out and not caring because I know in the back of my head that somewhere in the lecture slides that day lies the answer to my question. It makes the course boring when information is just thrown at you off a slide and there's no discussion or real application. This course is the opposite. The lectures were engaging, and important. It wasn't as though we were left alone; Dr. Hogue and our TAs Mina and Dan are approachable and will help steer you in the right direction any time you ask, but the course requires students to put actual thought and effort into their work. There's no BS in this course, and you can't BS your way out of it.

All in all I think the course is well designed, and I can surely say that I learned more in this course than I did in all my other classes this semester put together.

Week 9 - Level-Up Showcase

Last week my team, Phoenix Development Studios, went to level up to show off our game The Next Dimension, a bullet-hell shooter inspired by Geometry Wars.

We decided we'd be getting our game ready for Level-Up around 3 weeks before we got approval from our Game Development Workshop Professor, Ken Finney. We buckled down and started getting our game ready to show off.

Most of the 3 weeks were spent cleaning up code, implementing keymapping and controller support, optimizing the game, and implementing some redesigns. But the one of the most significant changes we made, at the last minute with just one line of code (yes, just one line of code, it is true...sort of), was the addition of a special background in our game's level select.

This addition to our game really increased its eye-catchiness. It also added to the affect that this was a sci-fi fantasy themed shooter.

After our game was approved by Professor Finney, we made on second change that completely changed the aesthetic of our game, and that was the inclusion of one new particle system that made it look as though explosion particles were warping together and flow towards the player.

When we got to level up, our main concern was that we wouldn't have a TV monitor to show off our game. Playing on a PC screen is fine, but when you want to grab peoples attention especially from a distance and within a sea of other people's awesome games, a small monitor doesn't exactly help. But luckily we were guaranteed one and we set up and all was fine...except some stupid errors in the release build of our game concerning optimization, which has since been fixed, but that meant we had to run the debug executable which is slightly slower than the current release build so it wasn't exactly a big deal.

Before the event started we had some students coming around asking us how we did the psychedelic background, and they were surprised to find out it was just one line of code (sort of). Once the event actually started, our visuals really caught the attention of those attending the event and we got more attention than we expected and many people enjoyed our game. We got a lot of feedback and some criticisms, some we already had planned for since we knew the limitations of our game, but mostly people just loved the aesthetic of the game, and the smooth controls.

By the end of the day though, my legs felt like they were going to fall off, but it was definitely worth it. Getting the opportunity to see other student's games from other schools was interesting, and I hope my team and I get the opportunity to go next year.

Week 8 - Scrolling Texture

The Next Dimension’s story revolves around travelling between different dimensions. In the story, the level select is explained as an inter-dimensional zone. To give the feeling that this is a surreal setting we decided to use a scrolling texture. The texture below is what was used to create the inter-dimensional space aesthetic:

The texture is perfectly aligned on both the right and left axes. The reason for this is so that the texture is mapped to a sphere, so the edges must be seamless otherwise it may break immersion. The texture is also mapped to the walls in each level, another reason the texture must be seamless. Because the texture is mapped to a sphere, it feels as though the world around the player is emitting cosmic rays and bursting, making it truly feel as though you are in a surreal fantasy world.

We also use another unique scrolling texture for the space level:

This texture used with the same shader gives a different feel do to its construction. In this case while playing the game, players tend to tilt their heads to the side and the effect pulls the player in. It truly gives the feeling that one is travelling through space.

Above is a video preview of the shader in action.

As seen above the scrolling texture truly adds to the effect of being in a surreal world.

Below is the shader code used to scroll the texture. It is a simple algorithm; we simply pass the total time elapsed since the beginning of the application and mutiply the UV coordinates to scroll the texture. The shader also samples from the texture twice, and scrolls both vertically and horizontally.

uniform sampler2D tex;

uniform float time;

uniform float speed;

void main()

{

gl_FragColor = texture2D(tex,vec2(gl_TexCoord[0].s + (time/-speed),gl_TexCoord[0].t)) + texture2D(tex,vec2(gl_TexCoord[0].t + (time/-speed),gl_TexCoord[0].s));

}

We also use another scrolling texture in our amazon inspired level. The level includes clouds that obscure the player's view of enemy spawners. The effect is meant to be one of wispy clouds flowing through the air as you travel through it, and I believe the affect was achieved perfectly.

Wispy clouds flowing through the air!

The shader algorithm used here is slightly different, as the texture is sampled twice, however it is only sampled with scrolling once.

uniform sampler2D tex;

uniform float time;

uniform float speed;

void main()

{

gl_FragColor = (texture2D(tex,vec2(gl_TexCoord[0].s + (time/-speed),gl_TexCoord[0].t)) + texture2D(tex,vec2(gl_TexCoord[0].s,gl_TexCoord[0].t)))/2;

}

Week 7 - NPR Shader

This week I completed my toon shader in GLSL, which was a lot easier than I thought. Below is a short clip of the toon shader in action.

Cel-shading

This was the part I perceived to be most difficult before I began writing the shader. It actually turned out to be quite simple. We simply do our compute our lighting as we normally would, then using the intensity at that point, we sample from a ramp to the diffuse to set of intensities in the map:

We use the sampled black-white intensity here and multiply it by the current geometry's color like we would with a regular diffuse. This achieves the cel-shading affect

Edge Detection

To complete the toon shading effect there is an edge pass. To do this we use a Sobel filter.

A Sobel filter essentially takes an image and using a convolution kernel, it detects differences in color in an image. Simply it detects edges. To do this, before we render our geometry we bind an FBO that has two color render targets, and one depth target. We render our scene to the FBO, passing the color to the first color target, and the normals to the second color target. Then, we use our edge detection program and pass all three render targets to our shader. We then use the sobel filter on the normals render target, and the depth render target and add the edges found in both together to get perfect outlines around all of our geometry.

A good example of toon shading in games, and also happens to be one of my favourites, is the Borderlands franchise. The toon shading in Borderlands is cel-shaded and uses edge detection, however the team at Gearbox took it a step further by creating their textures in such a way that it made it look like it was indeed a comic book. Their characters are also modeled in a non-realistic way which makes the use of the edge detection less obvious while not detracting from the toon effect. There are also some post-processing effects to bring out the richness of the colors, and when playing it the game really does feel like you are in a semi-realistic cartoon world.

Week 6 - Per-fragment Lighting

This week I completed a shader that uses the Blinn-Phong lighting model to light the scene. Below is a clip of the shader in action with 5 animated different colored lights.

Diffuse:

The diffuse component is essentially the intensity of light at a point on a plane/model. This is known as the Lambertian Reflection. Lambert's cosine law states that the instensity of light is proportional to the cosine of the angle formed between the light's direction and the surface normal.

Specular:

Using specular reflection in our model allows us to add specular highlights to our lighting model. Specular highlights are the bright spots on shiny objects when they are lit. In my lighting calculations I have chosen to go with the Blinn-Phong lighting model which bases the intensity of the specular component on the cosine angle of the half-vector and the normal.

Below is my GLSL shader function used to compute the total intensity and final color for one light.

vec3 returnTotalLight(Light light)

{

vec3 P = pos.xyz;//vertex positon

vec3 N = normalize(normal);//eye position in camera space

vec3 V = normalize(eye.xyz - P);//view direction

vec3 L = normalize(light.position - P);//light direction

vec3 H = normalize(L + V);//half vec for spec term

float specularLight = pow(max(dot(N,H),0), shininess);

float diffuseLight = max(dot(N,L),0);

vec3 diffuse = vec3(light.color *diffuseLight);

if(diffuseLight<=0)

{

specularLight = 0;

}

vec3 specular =vec3( light.color * specularLight);

return vec3(specular + diffuse);

};

Saturday, March 30, 2013

Week 5 - Brightness/Contrast & Curves Adjustments

Brightness & Contrast Control

Last week I completed 3 post-processing shaders. I completed a shader for controlling intensity profiles, a shader for adjusting the brightness and contrast of an image, and a shader for curves adjustment. This blog will focus on the brightness and contrast shader as well as the curves adjustment shader.

When changing the brightness of an image, a constant is added or subtracted from the luminance of every pixel in the scene.

Changing the contrast of an image changes the range of luminance values present. It essentialy expands or compresses the color of a pixel around a constant.

Below is the shader code for brightness and contrast control:

uniform float brightness;
uniform float contrast;
uniform sampler2D scene;

void main()
{
//sample scene color
vec3 color = texture2D(scene, gl_TexCoord[0].st).rgb;

//contrast color
vec3 colorContrasted = (color - 0.5) * contrast + 0.5;

//and brightness constant
vec3 bright = colorContrasted + vec3(brightness,brightness,brightness);

gl_FragColor.rgb = bright;
}

Below are screenshots of the shader:

Brightness = 0, Contrast = 1

Contrast Below 1

Contrast Above 1

Brightness Increased ( > 0)

Brightness Decreased ( < 0)

The curves adjustment shader uses a color map/ramp to remap the colors to a new set of colors based on the map. Below is the shader code:

uniform sampler2D scene;
uniform sampler2D ramp;

void main()
{
vec3 color = texture2D(scene, gl_TexCoord[0].st).rgb;
vec3 outColor;
outColor.r = texture2D(ramp, vec2(color.x , 0.0)).r;
outColor.g = texture2D(ramp, vec2(color.y , 0.0)).g;
outColor.b = texture2D(ramp, vec2(color.z , 0.0)).b;
gl_FragColor.rgb = outColor;
}

To remap the color we use the RGB values of the color to sample for the color ramp. This is done here:

outColor.r = texture2D(ramp, vec2(color.x , 0.0)).r;
outColor.g = texture2D(ramp, vec2(color.y , 0.0)).g;
outColor.b = texture2D(ramp, vec2(color.z , 0.0)).b;

We then simply output the color and it appears as so

Curves Adjustment

And the color ramp used to remap the color: