# OpenGL Fill distance with quads

## Recommended Posts

hockeyman    130
I am developing paint app. User can draw with mouse on my OpenGL view. He draws textured quads (textured to look like circle). But when he drags mouse faster there appears spacings between quads. So I calculate distance between previous point and current point, and if its bigger than something I need to add more quads to that distance automatically. How can I do that? I'm using vertex array.

Code:
[CODE]int count = [vertices count] * 8;
GLVertices = (GLfloat *)malloc(count * sizeof(GLfloat));
int currIndex = 0;
for (NSValue *locationValuetl in vertices) {
CGPoint loc = locationValuetl.pointValue;
GLVertices[currIndex++] = loc.x;
GLVertices[currIndex++] = loc.y;

}
for (NSValue *locationValuetr in vertices) {
CGPoint loc = locationValuetr.pointValue;
GLVertices[currIndex++] = loc.x;
GLVertices[currIndex++] = loc.y;
}
for (NSValue *locationValuell in vertices) {
CGPoint loc = locationValuell.pointValue;
GLVertices[currIndex++] = loc.x;
GLVertices[currIndex++] = loc.y;
}
for (NSValue *locationValuelr in vertices) {
CGPoint loc = locationValuelr.pointValue;
GLVertices[currIndex++] = loc.x;
GLVertices[currIndex++] = loc.y;
}
int distance1 = sqrt(GLVertices[currIndex - 1]*GLVertices[currIndex - 9] + GLVertices[currIndex]*GLVertices[currIndex - 8]);
if (distance1 > brushSize/4) {
//need to do something here
[/CODE]

Image of current result:

[img]http://s9.postimage.org/5dso9ff33/Screen_Shot_2012_07_09_at_1_33_57_PM.png[/img]

Can someone help me?

##### Share on other sites
[quote]So I calculate distance between previous point and current point, and if its bigger than something I need to add more quads to that distance automatically.[/quote]
Uh.....call your draw function for the space in between each brush...

You know how to draw quads. You know how to draw multiple quads. It sounds like you can draw a few more....

##### Share on other sites
hockeyman    130
I can, but I don't know how to do it in this situation. Because my vertex array object depends on user actions. I mean, points are being added wherever user drags pressed mouse. So I don't know how to tell my program where to draw these additional quads if distance is bigger than something.

If last two quads vertexes in my vertex array is
[CODE]
(x1,y1)[top left]
(x2,y2)[top right]
(x3,y3)[bottom right]
(x4,y4)[bottom left]
[/CODE]

and
[CODE]
(x5,y5)[top left]
(x6,y6)[top right]
(x7,y7)[bottom right]
(x8,y8)[bottom left]
[/CODE]

and distance between them is bigger than my allowed size (lets say I'm counting distance between [bottom right] points to know the distance between quads), then how to add for example 3 quads (12 vertexes) to my vertex array where they are needed (between these two quads)? I cant't know where user will be drawing, so I don't know exactly where additional quads will be needed. Edited by hockeyman

##### Share on other sites
[quote]I cant't know where user will be drawing[/quote]
Based on your drawing you are trying to fill the points between the last brush position and the current. So you know where the user is drawing.

The only way to fix this is to draw a brush for each pixel in between the circles. If you use a distance bigger than that you won't get a brush stroke, you will get more of a caterpillar looking brush, like the medium drawing you posted.

##### Share on other sites
hockeyman    130
[quote]The only way to fix this is to draw a brush for each pixel in between the circles.[/quote]

How to do it? Is there any tutorials or some useful documentation/information on the internet or something? Edited by hockeyman

##### Share on other sites
Simple way without using a line drawing algorithm like Bresenham:

Create a 2D vector between start and end brush.
Find the length in pixels of that line using pythagorean theorem.
float timeStep = 1.0/length in pixels
float time = 0;
for(int i = 0; i < length in pixels; i++)
{
Vec2 fillPos = start + time*brushvector;
time += timeStep;
}

When time = 1, the fill pos is the endpoint
When time = .5, the fill pos is halfway to the endpoint Edited by dpadam450

##### Share on other sites
hockeyman    130
Many many thanks for you. Just met the problem that as I see vectors aren't built-in in Objective-c. Maby you can suggest any library for it? And another question. Now with your code I have path witch should be filled. How could I do it? Any openGL commands or something to tell it to draw quads in every location from point A to point B?

## Create an account

Register a new account

• ### Similar Content

• Hello. I'm Programmer who is in search of 2D game project who preferably uses OpenGL and C++. You can see my projects in GitHub. Project genre doesn't matter (except MMO's :D).

• Hello, My name is Matt. I am a programmer. I mostly use Java, but can use C++ and various other languages. I'm looking for someone to partner up with for random projects, preferably using OpenGL, though I'd be open to just about anything. If you're interested you can contact me on Skype or on here, thank you!
Skype: Mangodoor408
• By tyhender
Hello, my name is Mark. I'm hobby programmer.
So recently,I thought that it's good idea to find people to create a full 3D engine. I'm looking for people experienced in scripting 3D shaders and implementing physics into engine(game)(we are going to use the React physics engine).
And,ye,no money =D I'm just looking for hobbyists that will be proud of their work. If engine(or game) will have financial succes,well,then maybe =D
Sorry for late replies.
I mostly give more information when people PM me,but this post is REALLY short,even for me =D
So here's few more points:
Engine will use openGL and SDL for graphics. It will use React3D physics library for physics simulation. Engine(most probably,atleast for the first part) won't have graphical fron-end,it will be a framework . I think final engine should be enough to set up an FPS in a couple of minutes. A bit about my self:
I've been programming for 7 years total. I learned very slowly it as "secondary interesting thing" for like 3 years, but then began to script more seriously.  My primary language is C++,which we are going to use for the engine. Yes,I did 3D graphics with physics simulation before. No, my portfolio isn't very impressive. I'm working on that No,I wasn't employed officially. If anybody need to know more PM me.

• By Zaphyk
I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?

• I'm trying to get some legacy OpenGL code to run with a shader pipeline,
The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
I've got a version 330 vertex shader to somewhat work:
#version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
Question:
What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?

Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.

• 22
• 15
• 18
• 10
• 18