I'm trying to draw a circle using Pixmap. To make the problem clearer, I'm filling the entire Pixmap area in white, then drawing the circle in a different color. Here is the code that I feel should work.
I'm setting the width/height of the Pixmap to twice the size of the radius of the circle.
Then I'm drawing a circle in the middle of the Pixmap at (radius, radius).
public static Texture circle(int radius, Color color) {
Pixmap pixmap = new Pixmap(radius * 2, radius * 2, Pixmap.Format.RGBA4444);
pixmap.setColor(Color.WHITE);
pixmap.fill();
pixmap.setColor(color);
pixmap.fillCircle(radius, radius, radius);
Texture texture = new Texture(pixmap);
pixmap.dispose();
}
Unfortunately, the Pixmap cuts off the circle on the right and bottom sides. For example:
If I increase the size of the Pixmap by 1 in both the width and height, then it looks fine:
I can just arbitrarily add an extra pixel but I'd like to understand why this is necessary. Why does setting the radius of the circle to X result in a diameter that is actually X + 1?
To get the result you want, the location of the circle's center would have to fall between two pixels, so that there are a similar number of whole pixels on either side of that location. My guess is that the Pixmap code defines a pixel's location to mean the center of a pixel. So the point (radius, radius) is closer to the right edge than the left, and (radius-1, radius-1) is closer to the left edge than the right. With this definition of location, the center of your circle should be at location (radius-.5, radius-.5).
If you have to put the center of the circle in the middle of a pixel, then it makes sense that you'd use the location (radius, radius) for the circle and that you'd need the width and height of the Pixmap to be (2*radius + 1, 2*radius+1). This way, there are the same number of pixels, radius+.5 pixels, on either side of the center of the circle. You might at that point want to draw a circle of radius radius + .5 if the library will take that.
Because it draws a circle centered on a pixel, not between pixels.
So the actual radius of the circle drawn is one more than passed in, a circle with radius 1 is drawn as (numbers are coordinates in this example):
012
0 X
1XCX
2 X
This technically has a radius of 1.5, but now it's centered on a pixel (C).
I am guessing this is to allow you to place it accurately, as if it actually had a radius of 2, you wouldn't be able to place the center on a pixel.
Related
I have not found answer for this question anywhere, so let's go.
What i expect:
I want to render rocket. Rocket is flying from given start point with evaluated angle. I'm evaluating angle like this:
getVelocity().angle() - 90f
My problem is to calibrate rocket position on top of the rocket. Image below shows how should it work:
In the top picture is how libgdx render not rotated texture region. In the bottom picture is what i expect: I want to move and rotate texture region with given angle to have (x,y) coordinate on the top of rocket.
What i have:
I tired to write method to draw sprite how i expect but i failed. I think it is caused due to fact that i don't understand documentation of this method.
Following manual:
void com.badlogic.gdx.graphics.g2d.SpriteBatch.draw(TextureRegion region, float x, float y, float originX, float originY, float width, float height, float scaleX, float scaleY, float rotation)
Draws a rectangle with the bottom left corner at x,y and stretching the region to cover the given width and height. The rectangle is offset by originX, originY relative to the origin. Scale specifies the scaling factor by which the rectangle should be scaled around originX, originY. Rotation specifies the angle of counter clockwise rotation of the rectangle around originX, originY.
My code:
public static void drawRotatedTex(SpriteBatch pmRenderer, TextureRegion pmTex, float pmPosX, float pmPosY, float pmAngle)
{
pmRenderer.begin();
pmRenderer.draw(
pmTex, pmPosX, pmPosY, -pmTex.getRegionWidth()/2, pmTex.getRegionHeight(), pmTex.getRegionWidth(), pmTex.getRegionHeight(), 1f, 1f, pmAngle);
pmRenderer.end();
}
Results:
It is moment of collision. As we can see coordinates are offset in relation to rocket.
I don't ask about full solution. For me will be sufficient if someone explain me (on drawing or something) like this method works.
EDIT
Moderation suggested that this question is duplicate of:
libgdx: Rotate a texture when drawing it with spritebatch
I read this topic, but it is not my solution. I know how to rotate my sprite by i don't have idea why coordinates of rocket are offset in relation to rocket top.
EDIT
Invocation of my drawRotatedTex from rocket class:
#Override
public void render(Renderer pmRenderer, float pmX, float pmY) {
SpriteBatch lvSpritebatch = pmRenderer.getSpriteBatch();
Sprite lvSprite = null;
if(mIsExploding)
{
if((lvSprite = mExplosion.getTexture()) != null)
{
lvSpritebatch.begin();
lvSpritebatch.draw(lvSprite, pmX + lvSprite.getWidth()/2, pmY - lvSprite.getHeight()/2);
lvSpritebatch.end();
}
}
else
{
lvSprite = mAnimation.getTexture();
RendererTools.drawRotatedTex(lvSpritebatch,lvSprite,pmX,pmY,getVelocity().angle() - 90f);
}
}
It is not very clear what you are asking, if it's only about moving the origin you would not need that much text. Anyway, I will take a shot at it.
If you want to accomplish what you have in your picture you setup your sprite like this:
sprite.setOrigin(s.getWidth()/2, s.getHeight()); //Centers sprite on top of image.
If I now rotate it in the draw method it rotates around the top center.
sprite.rotate(5);
sprite.draw(batch);
Despite being rotated around the center top of itself it remains position remains the same. If I would set the origin far away from the image and rotate it then the image would travel very far but the position remains the same. Still if you would move it's position 10 pixels to the right the image (wherever it may be) will be moved to the right.
Hope this helps.
Im trying to draw an arc that stretches around part of the circle. Im confused on how to use the DrawArc method. I read few articles online and to simply put, im confused on how the parameters exactly work. My circle is centered at 100, 100 with radius of 50. How would i use the drawArc method to draw an arc that overlaps the circle ? Any thoughts would be highly appreciated
Reading articles is good, but you should always read a method's documentation.
The drawArc method does not take a center and radius as arguments. Instead, it takes a rectangle. The x and y arguments are the upper-left corner of that rectangle; the width and height are the horizontal and vertical diameters of your arc's ellipse.
You can just do the math yourself:
int centerX = 100;
int centerY = 100;
int radius = 50;
graphics.drawArc(centerX - radius,
centerY - radius,
radius * 2,
radius * 2,
startAngle,
span);
Note that the final argument is the number of degrees the arc spans, not the absolute end angle.
I have a problem with JSlider in Java I have drawn a circle A, and I want to put ANOTHER circle B inside the first circle A. I want to place the CENTRE of the second circle B at the same coordinate with the centre of the first circle A, and then I want to use JSlider to INCREASE or DECREASE the radius of circle B. The trouble is, when you increase or decrease the slider, the CENTRE of circle B does not stay aligned with the centre of A. Basically, I want two circles with the SAME centre. Can someone point out my mistake, please?
slider1 = new JSlider(JSlider.HORIZONTAL,10,100,10);
window.add(slider1);
slider1.addChangeListener(this);
Graphics paper = panel.getGraphics();
int slider1Value = slider1.getValue();
paper.setColor(Color.white);
paper.fillRect(0, 0, 500, 500);
paper.setColor(Color.pink);
paper.fillOval(20,20,100,100); // this is circle A
paper.drawOval(60,60,slider1Value,slider1Value); // this is circle B slider
Because you have to change position of top-left "corner" of circle. If you change radius, the circle is bigger/smaller so it's obvious if you don't change position of top-left cornet, centers of 2 circles won't be aligned
Theory
From Graphics.drawOval() javadoc. When you draw a circle their (x,y) coordinates are not its center but its top-left corner. In order to make your B circle aligned with A circle, you need to calculate its (x,y) coordinates relatives to the last one:
Circle A: (x,y) = (20,20); diameter = 100 ==> radius = 50; center = (x + radius, y + radius) = (70,70)
Well, you have your center now: (70,70). Now, slider1Value is your new radius so you need to calculate circle B (x,y) coordinates:
Circle B: center = (70,70); (x,y) = (centerX - radius, centerY - radius) = (70 - slider1Value, 70 - slider1Value)
Finally, circle B width and height are equals to its diameter:radius * 2 = slider1Value * 2.
Facts
Make this change and it will work like a charm:
paper.drawOval(70 - slider1Value, 70 - slider1Value, 2*slider1Value, 2*slider1Value);
I am translating in my main class' render. How do I get the mouse position based on the translation?
public void render(GameContainer gc, Graphics g)
throws SlickException
{
float centerX = 800/2;
float centerY = 600/2;
g.translate(centerX, centerY);
g.translate(-player.playerX, -player.playerY);
gen.render(g);
player.render(g);
}
playerX = 800 /2 - sprite.getWidth();
playerY = 600 /2 - sprite.getHeight();
I update the player position on keydown by .2f * delta
Picture to help with explanation
i92.photobucket.com/albums/l22/occ31191/Untitled-4.png
World coordinates = camera position + mouse position
Camera position is calculated/explained in my answer to this question: Slick2D and JBox2D. How to draw
You're making a tile-based game, where each tile seems to have the same size. For this case, you don't need a generalized unprojection.
Imagine the complete map. The viewport shows only a portion of it; somewhere you need to store the (x,y) offets of the viewport into the complete map. Since the mouse coordinates are relative to the viewport, you need to add this offset to the mouse coordinates. Now, you can easily get the tile coordinates by using modulo operations on the shifted mouse coordinates with the tile's width and height.
Effectively, this is a coordinate transformation of window coordinates to tile coordinates.
The issue involves an Android Path shape. It's a triangle that I'm using as an arrow to point towards objects on a screen Canvas. This is for a 2d game. player in the middle of the screen, objects around him and offscreen.
These arrows are supposed to rotate around the center of the screen, with a radius so that they rotate in a circle around the player. The arrows point towards objects that the player needs to move towards.
What I have right now is somewhat working, but the arrows are zipping around the circle at ridiculous speeds. Funny enough, they're pointing in the right direction, but they aren't staying at the right point on the circle. (if arrow is pointing northeast, arrow should be on the northeast part of the circle, etc)
I'm sure it's because of the math. I'm probably using atan2 wrong. Or canvas.translate wrong. Or maybe I shouldn't be using atan2 at all. Help! :)
Here is the code:
// set the shape of our radar blips
oBlipPath.moveTo(0, -5);
oBlipPath.lineTo(5, 0);
oBlipPath.lineTo(0, 5);
// Paint all the enemies and radar blips!
for(int i=0; i<iNumEnemies; i++){
if (oEnemies[i].draw(canvas, (int)worldX, (int)worldY)){
//calculate the degree the object is from the center of the screen.
//(user is the player. this could be done easier using iWidth and iHeight probably)
//we use a world coordinate system. worldY and worldX are subtracted
fDegrees = (float)Math.toDegrees(Math.atan2((oEnemies[i].getEnemyCenterY()-worldY)-user.getShipCenterY(), (oEnemies[i].getEnemyCenterX()-worldX)-user.getShipCenterX()));
canvas.save();
//get to the center
canvas.translate((iWidth / 2) , (iHeight / 2) );
//move a little bit depending on direction (trying to make arrows appear around a circle)
canvas.translate((float)(20 * Math.cos(fDegrees)), (float)(20* Math.sin(fDegrees)));
//rotate canvas so arrows will rotate and point in the right direction
canvas.rotate(fDegrees);
//draw arrows
canvas.drawPath(oBlipPath, oBlipPaint);
canvas.restore();
}
}
Affine transformations are are not commutative. They are typically applied in an apparent last-specified-first-applied order. As an alternative, consider the rotate() variation that rotates about a point.
Well, I've got it doing what I wanted, but I don't really know how. I threw in some random numbers until things showed up on the screen the way I wanted. If anyone wants to clue me in as to a better way to do this, I'm all ears.
The code:
// set the shape of our radar blips
oBlipPath.moveTo(0, -5);
oBlipPath.lineTo(6, 0);
oBlipPath.lineTo(0, 5);
oBlipMatrix.setRotate(45, 0, 0);
oBlipPath.transform(oBlipMatrix);
// Paint all the enemies and radar blips!
for(int i=0; i<iNumEnemies; i++){
oEnemies[i].draw(canvas, (int)worldX, (int)worldY);
if (oEnemies[i].bActive){
//calculate the degree the object is from the center of the screen.
//(user is the player. this could be done easier using iWidth and iHeight probably)
//we use a world coordinate system. worldY and worldX are subtracted
fDegrees = (float)Math.toDegrees(Math.atan2((oEnemies[i].getEnemyCenterY()-worldY)-(iHeight / 2), (oEnemies[i].getEnemyCenterX()-worldX)-(iWidth / 2)));
canvas.save();
//get to the center
canvas.translate((iWidth / 2 + 50) , (iHeight / 2 + 50) );
//move a little bit depending on direction (trying to make arrows appear around a circle)
//canvas.translate((float)(20 * Math.cos(fDegrees)), (float)(20* Math.sin(fDegrees)));
//rotate canvas so arrows will rotate and point in the right direction
canvas.rotate(fDegrees-45, -50, -50);
//draw arrows
canvas.drawPath(oBlipPath, oBlipPaint);
canvas.restore();
}
}
For whatever reason, I have to subtract 45 degrees from the canvas rotation, but add 45 degrees to the matrix rotation of the path shape. It works, but why?! :)