I am a student studying Processing.
I watch an example video I recently discovered to study Processing, and I ask a question because there is a concept that is difficult to understand.
rotate the triangle so that the top vertex of the triangle always faces the point.
Also, a line that runs vertically from the midpoint of the base of the triangle must be connected to the point.
I am not sure where to start fixing the problem.
If you understand the problem, I would appreciate it if you could provide a brief explanation and code.
It looks like a great demonstration of the rotate function, perhaps combined with the translate function. Look at this Processing tutorial for a good description of what you can do with these functions.
To get the desired effect, the program can select a random angle and a random distance between the triangle and the circle. Using the rotate and translate functions, you can basically draw the triangle, circle & line at fixed coordinates and have Processing do the calculations for you (except the distance between the triangle and the circle). The program could look like this:
void settings() {
size(800, 600);
}
void setup() {
frameRate(2);
}
void draw() {
background(128);
float angle = random(-QUARTER_PI, QUARTER_PI);
float ballDistance = random(100, 400);
translate(width / 2, height - 28);
rotate(angle);
noStroke();
fill(255, 0, 0);
circle(0, -ballDistance, 12);
stroke(120, 200, 120);
line(0, 0, 0, -ballDistance);
noStroke();
fill(0, 0, 255);
triangle(-16, 0, 16, 0, 0, -64);
}
Related
I have a complex 3D plot with some text on rollover. It's already a bit cluttered so I'd like to have the text always be in front of all the plot parts. Like here:
Right now, when I hover over some points in the background, the text is sometimes hidden behind plot components, like here:
How can I force the text to always be in the front and facing the camera (which it already is right now).?
Use pushMatrix()/popMatrix() to isolate coordinate spaces: one for the 3D graphics, another for the 2D elements on top:
void setup(){
size(300, 300, P3D);
sphereDetail(9);
noFill();
stroke(255);
textSize(21);
textAlign(CENTER);
}
void draw(){
background(0);
// 3D
pushMatrix();
translate(width * 0.5, height * 0.5, 0);
rotateX(map(mouseY, 0, height, -PI, PI));
rotateY(map(mouseX, 0, width, PI, -PI));
sphere(150);
popMatrix();
// 2D
pushMatrix();
text((int)frameRate, mouseX, mouseY);
popMatrix();
}
(The indenting is not required, just visually emphasising coordinate space nesting.
The last push/pop may not be needed for such as simple example, but is useful if you have more 2D/3D things happening on top of what's already been drawn)
For more info checkout the 2D Transformations Tutorial.
Additionally you might find the PeasyCam library useful.
To draw 2D text on top you'd do something like:
camera.beginHUD();
// draw 2D overlays here
camera.endHUD(); // back to 3D
Note: I also asked this question on the Processing forum here.
I have this sample code:
PGraphics pg;
void setup() {
size(400, 500);
pg = createGraphics(width, height);
pg.noSmooth();
pg.beginDraw();
pg.background(0, 0, 255);
pg.endDraw();
}
void draw() {
if (mousePressed) {
pg.beginDraw();
pg.stroke(255, 254);
pg.point(mouseX, mouseY);
pg.endDraw();
}
image(pg, 0, 0, width, height);
}
I would expect this code to show a point wherever the user presses the mouse. Instead, I am only able to see points in a couple rectangular areas:
If I remove the call to pg.noSmooth() or if I remove the alpha value in the pg.stroke() call, then it works fine:
If I replace the pg.point() call with pg.ellipse() or pg.rect() then it also works fine.
It seems like the combination of using a PGraphics, the noSmooth() function, the point() function, and an alpha value results in this buggy behavior. I’ve tried in Processing 3.3 and Processing 3.5.2 and I see the same behavior in both.
Am I missing something obvious?
After a wee bit of digging up turns out the JAVA2D renderer draws a point as a diagonal line(line(x, y, x + EPSILON, y + EPSILON);) with a very very very small spacing (static final float EPSILON = 0.0001f;). My guess is this particular configuration the lack aliasing might mean both points of this diagonal line land on the same pixel and end up not being rendered on the top right area which. Why that area and how come this small distance I don't know, but it sounds a bit like the headaches Jakub Valtar and Andres Colubri had to deal with.
FWIW here's a hacky workaround: using a larger distance that does get rendered with transparency and no aliasing:
PGraphics pg;
void setup() {
size(400, 500);
noSmooth();
pg = createGraphics(width/20, height/20);
pg.beginDraw();
// just for debug purposes: rectangle with edge
pg.fill(0, 0, 255);
pg.rect(0,0,pg.width-1,pg.height-1);
pg.stroke(255,255,255, 128);
pg.endDraw();
}
void pointNoSmooth(PGraphics pg, float x,float y){
pg.beginShape();
pg.vertex(x,y);
pg.vertex(x + 0.75,y);//any less than 0.75 distance between vertices and there's nothing to render with aliasing
pg.endShape();
}
void draw() {
background(255);
if (mousePressed) {
pg.beginDraw();
pointNoSmooth(pg,mouseX,mouseY);
pg.endDraw();
}
// render upscaled
image(pg, 0, 0, width, height);
// render small preview in TL corner
image(pg,0,0);
}
Notice that I've set the PGraphics resolution 20 times smaller, then drawn it upscaled so it's easier to see where the pixels land on the PGraphics. I'm not scaling the mouseX,mouseY coordinates though, so you'll need to draw in the small top left preview when testing. That 0.75 distance does the trick: from what I've tested, anything smaller than 0.7499995 starts acting buggy again.
I am trying to create concentric circles filled with lines moving in opposite directions (that follow the mouse). I can't figure out how to fill only the circles with the lines -- I used a for-loop to make lines, and want to cut them off outside of the radius of the circles. Basically, I am trying to fill the circles with a pattern of lines.
This is my code:
float r = 0;
float startAngle;
float density;
float radius;
void setup() {
size(500, 500);
background(255);
stroke(150, 0, 150);
}
void draw() {
int[] s = {
500, 325, 200, 100, 50, 25
};
for (int i = 0; i < 500; i = i+5) {
line(0, i, 500, i);
if(i > s[0]) {
noStroke();
}
}
translate(width/2, height/2);
rotate(r);
r = r + .01;
fill(0);
ellipse(0, 0, s[0], s[0]);
fill(50);
ellipse(0, 0, s[1], s[1]);
fill(100);
ellipse(0, 0, s[2], s[2]);
fill(150);
ellipse(0, 0, s[3], s[3]);
fill(200);
ellipse(0, 0, s[4], s[4]);
fill(255);
ellipse(0, 0, s[5], s[5]);
}
Any help would be appreciated!
It's hard to help with general "how do I do this" type questions. Stack Overflow is designed for more specific "I tried X, expected Y, but got Z instead" type questions. But I'll try to help in a general sense.
The best advice I can give you is to start smaller. Break your problem down into smaller pieces and take those pieces on one at a time.
For example, instead of starting with your whole program that shows multiple circles, why not start with a simpler example program that just shows a single circle? Try to get a pattern to display inside of that.
Like everything in programming, there are multiple ways to do that.
Option 1: You could probbaly use basic geometry and trig to figure out where the points should be on the circle, then draw them based on those points. The cos() and sin() functions would probably come in handy with this approach.
Option 2: You could also use image masking techniques. For example, you could create a texture of lines, and then use a circular mask to isolate a cirlce of those lines. The texture() function or the PImage#mask() functions would be your friends here.
Try out those approaches to see which one you like best. The Processing reference is your best friend: for example, here is a reference on the texture() function, and here is a reference on the PImage#mask() function. Then if you get stuck on a specific step, you can post a MCVE of just that step, and we'll go from there. Good luck.
I've got a big sphere. There is a red dot that moves around the sphere. I want to follow that red dot as it moves around to sphere. So my camera has to move with the red dot. But there is a problem. Right now, what I'm experiencing is what is shown in exhibit B. I want my animation to realize the point of view shown in exhibit A.
Here is the code I have so far. I think it's pretty simple. I have 3 variables that control where my eye is, and I have 3 variables that control where the target is. The red dot is also located at the target position. I added 2 planes in x-y which helped me not get too confused as the thing was spinning.
Here is a fiddle:
https://jsfiddle.net/da8nza6y/
float radius = 1000;
float view_elevation = 1500;
float target_elevation = 300;
float x_eye;
float y_eye;
float z_eye;
float x_aim;
float y_aim;
float z_aim;
float h;
float theta;
void setup() {
size(600, 600, P3D);
theta = 0;
h = 30;
}
void draw() {
theta += 0.5;
theta = theta%360;
x_eye = (radius+view_elevation)*cos(theta*PI/180);
y_eye = 0;
z_eye = (radius+view_elevation)*sin(theta*PI/180);
x_aim = (radius+target_elevation)*cos((theta+h)*PI/180);
y_aim = 0;
z_aim = (radius+target_elevation)*sin((theta+h)*PI/180);
camera(x_eye, y_eye, z_eye, x_aim, y_aim, z_aim, 0, 0, -1);
background(255);
// the red dot
pushMatrix();
translate(x_aim, y_aim, z_aim);
fill(255, 0, 0, 120);
noStroke();
sphere(10);
popMatrix();
// the big sphere
noStroke();
fill(205, 230, 255);
lights();
sphere(radius);
// the orange plane
pushMatrix();
translate(0, 0, 10);
fill(255, 180, 0, 120);
rect(-2000, -2000, 4000, 4000);
popMatrix();
// the green plane
pushMatrix();
translate(0, 0, -10);
fill(0, 180, 0, 120);
rect(-2000, -2000, 4000, 4000);
popMatrix();
}
So the pickle is that, it seems like the moment the red dot (whose location in the x-z plane is given by the angle (theta+h) and distance (radius+target_elevation) from the origin) crosses the x-y plane, everything gets flipped upside-down and backwards.
Now, I have tried to control the last 3 variables in the camera() function but I'm getting confused. The documentation for the function is here:
https://processing.org/reference/camera_.html
Can anyone see a solution to this problem?
Also, I'm sure I could just rotate the sphere (which I can do) and not have these problems, but I'm sure where I'm going with this animation and I feel like there will be things to come that will be easier with this method. Though I could be mistaken.
I believe I've solved my own problem.
I've added the following lines in draw, before calling the camera() function:
if ((x_eye- x_aim) < 0) {
z_orientation = 1;
} else {
z_orientation = -1;
}
I noticed that it wasn't (theta+h) that was triggering the flip, but the relative positions of the view and target.
Here is an updated fiddle:
https://jsfiddle.net/da8nza6y/1/
As a small homework to get into Processing, I had to write some code to get the following:
Using
public void setup() {
size(300,200);
noFill();
rect(100, 20, 40, 80);
ellipseMode(CENTER);
fill(#000000);
ellipse(width/2, height/2, 5,5);
noFill();
translate(width/2, height/2);
rotate(radians(65));
rect(-20, -40, 40, 80);
}
public void draw() {
}
this worked very good, so far. But I don’t like that I had to change the coordinates inside of the bottom rect instruction in order to get the rotation right. I know that by rotating you don’t rotate single elements but in fact the whole coordinate system.
What I don’t know is which values to put into the translate instruction to have the output be like in the picture above while also still using the same coordinates within the rect command.
The task is already done with the code I used, I just don’t like it too much. So this isn’t mere asking for somebody else doing my homework but pure interest.
EDIT: More generalised attempt of a question: How do I know which values to pit into translate before rotate to get whatever result I want? Is there a way to calculate them? For sure, it’s not just trying out, is it?
A lot of the confusion in processing is the coordinate system. In Processing the origin (0,0) is at the top left of the screen and only positive coordinates display on the screen. The very common workaround for this is to call:
translate(width/2, height/2);
at the beginning of your void draw() method. That way 0,0 is now at the center of the sketch, and any subsequent methods called such as rotate(radians(65)) will take action from the center of the sketch.
This is also good because sketches that use the P3D or OPENGL renderer often call translate to change the coordinate system into something that is easier to use. For example an object at 0,0 or 0,0,0 is at the center and it makes it easier to orbit the camera around the object or have the object rotate around its center.
another popular way of drawing objects would be to set the origin as above and instead of giving the coordinates of each object, i.e. rect(-100, -50, 50, 50) is to use popMatrix() and pushMatrix before a translate before drawing each object at 0,0 as illustrated below:
translate(width/2, height/2);
pushMatrix();
translate(-100, -50);
rect(0,0,50,50);
popMatrix();
This is a good approach to use in a 2d renderer if you think you might move to 3d renderer eventually, because you can easily replace rect() with box() or sphere() or create your own method or object that draws geometry assuming the origin is at 0,0.
If you replace the x and y coordinates with variables or iterate through an array in a for loop it becomes very easy to draw hundreds or thousands of shapes in either 2d or 3d with minimal effort and minimal rewriting of the code.
update: added clarification for the original poster, per their comment.
I have changed the problem slightly to show you how I would approach this. I am showing the translate / rotate method I described above using push and pop matrix. I am just guessing at the values, but if you want something pixel accurate you can take measurements in an image editing program like photoshop or preview.
translate(180, 150);
rect(0, 0, 180, 80);
translate(185, 170);
rotate(radians(65));
rect(0, 0, 180, 80);
translate(180, 250);
ellipse(0, 0, 8, 8);
Putting it all together with pushMatrix() and popMatrix().
void setup(){
size(400,400);
}
void draw(){
// rect1
noFill();
pushMatrix();
translate(180, 150);
rect(0, 0, 180, 80);
popMatrix();
// rect2
pushMatrix();
translate(185, 170);
rotate(radians(65));
rect(0, 0, 180, 80);
popMatrix();
// ellipse
fill(0);
pushMatrix();
translate(180, 250);
ellipse(0, 0, 8, 8);
popMatrix();
}
in my particular example, know how to translate and rotate to get the
result in the picture without changing the rectangle coordinates?
Well, you need to draw at origin to use rotate properly, so you are just dealing with the origin of the rect... As it is in your code, the default, the origin is the upper left corner, so you made an off set (from (0,0)) to draw it's centre, not the corner, at coordinate(0,0), then rotate by the middle. Well done. It is not coincidence that the values you found was minus half rect width(-20) and minus half rect height(-40). If you change to rectMode(CENTER) than you can just draw at (0,0). The same applies to translate, you can just translate to the desired point, the center of the screen, where there is the ellipse. What is done using half width and half height...
look:
public void setup() {
size(300, 200);
smooth();
ellipseMode(CENTER);
rectMode(CENTER);
noFill();
// here converting the coordinates to work with CENTER mode
//could have changed the rect mode just after this
// but i kept as an illustration
int rwidth = 40;
int rheight = 80;
int xpos = 100 + rwidth/2;
int ypos = height/2 - rheight/2 ;
rect(xpos, ypos, rwidth, rheight);
fill(#000000);
ellipse(width/2, height/2, 5, 5);
noFill();
pushMatrix();
translate(width/2, height/2);
//draw at origin gray
stroke(150);
rect(0, 0, 40, 80);
// then rotate
rotate(radians(65));
// draw again black
stroke(0);
rect(0, 0, 40, 80);
popMatrix();
// here using the cordinates calculated before as a translate value
// we draw at origin, but it appears at same place
stroke(230,230,100);
// a bit to the left...
translate(xpos-2, ypos-2);
rect(0, 0, 40, 80);
}
Rotation is aways applied to origin point (0,0), so you want to draw your axis for rotating at origin. Or move the coordinate system origin, to your axis. It is indeed confusing. When using transformations I tend to draw at origin always. Try this to see if it makes things more clear... or less :)
Also there is push/popMatrix() to control the scope of transformations...
public void setup() {
size(300, 380);
smooth();
}
public void draw() {
background(0);
stroke(255);
//use push/pop Matrix to control scope of translate and rotate
pushMatrix();
//move coordinates system origin to center of screen
translate(width/2, height/2);
// rotate with origin as axis
rotate(radians(mouseY));
//draw at origin (now temp moved to center of screen)
// white line
line(0, 0, 150, 0);
// here all coordinate system is back to normal
popMatrix();
//draw with normal system red line at origin
stroke(255, 0, 0);
line(0, 0, 150, 0);
//draw with normal system blue line at centre
stroke(0, 0, 255);
line(width/2, height/2, width/2 + 150, height/2);
}