How can i rotate an image from the center rather than the corner in pygame?
Rotate the sprite then set the center of the new rect to the center of the old rect. This way the new one has the same center when you're done, making it look like it rotated around the center.
Here's an example function from the pygame wiki:
def rot_center(image, rect, angle):
"""rotate an image while keeping its center"""
rot_image = pygame.transform.rotate(image, angle)
rot_rect = rot_image.get_rect(center=rect.center)
return rot_image,rot_rect
And here's how you would use it in your example:
# Draw ship image centered around 100, 100
oldRect = shipImg.get_rect(center=(100,100))
screen.blit(shipImg, oldRect)
# Now rotate the ship and draw it with the new rect,
# which will keep it centered around 100,100
shipImg, newRect = rot_center(shipImg,oldRect,-90)
screen.blit(shipImg, newRect)
How to rotate an image around its center while its scale is getting larger(in Pygame)
Short answer:
Store the center of the source image rectangle and update the center of the rotated and zoomed image rectangle after the rotation and zoom operation, by the stored center position. Rotate and zoom the image by pygame.transform.rotozoom()
:
def blitRotateCenter(surf, image, topleft, angle, scale):
center = image.get_rect(topleft = topleft).center
rotated_image = pygame.transform.rotozoom(image, angle, scale)
new_rect = rotated_image.get_rect(center = center)
surf.blit(rotated_image, new_rect.topleft)
Long Answer:
An image (pygame.Surface
) can be rotated by pygame.transform.rotate
.
If that is done progressively in a loop, then the image gets distorted and rapidly increases:
while not done:
# [...]
image = pygame.transform.rotate(image, 1)
screen.blit(image, pos)
pygame.display.flip()
This is cause, because the bounding rectangle of a rotated image is always greater than the bounding rectangle of the original image (except some rotations by multiples of 90 degrees).
The image gets distort because of the multiply copies. Each rotation generates a small error (inaccuracy). The sum of the errors is growing and the images decays.
That can be fixed by keeping the original image and "blit" an image which was generated by a single rotation operation form the original image.
angle = 0
while not done:
# [...]
rotated_image = pygame.transform.rotate(image, angle)
angle += 1
screen.blit(rotated_image, pos)
pygame.display.flip()
Now the image seems to arbitrary change its position, because the size of the image changes by the rotation and origin is always the top left of the bounding rectangle of the image.
This can be compensated by comparing the axis aligned bounding box of the image before the rotation and after the rotation.
For the following math pygame.math.Vector2
is used. Note in screen coordinates the y points down the screen, but the mathematical y axis points form the bottom to the top. This causes that the y axis has to be "flipped" during calculations
Set up a list with the 4 corner points of the bounding box:
w, h = image.get_size()
box = [pygame.math.Vector2(p) for p in [(0, 0), (w, 0), (w, -h), (0, -h)]]
Rotate the vectors to the corner points by pygame.math.Vector2.rotate
:
box_rotate = [p.rotate(angle) for p in box]
Get the minimum and the maximum of the rotated points:
min_box = (min(box_rotate, key=lambda p: p[0])[0], min(box_rotate, key=lambda p: p[1])[1])
max_box = (max(box_rotate, key=lambda p: p[0])[0], max(box_rotate, key=lambda p: p[1])[1])
Calculate the "compensated" origin of the upper left point of the image by adding the minimum of the rotated box to the position. For the y coordinate max_box[1]
is the minimum, because of the "flipping" along the y axis:
origin = (pos[0] + min_box[0], pos[1] - max_box[1])
rotated_image = pygame.transform.rotate(image, angle)
screen.blit(rotated_image, origin)
To define a pivot on the original image, the "translation" of the pivot in relation to the upper left of the image has to be calculated and the "blit" position of the image has to be displaced by the translation.
Define a pivot e.g. in the center of the image:
pivot = pygame.math.Vector2(w/2, -h/2)
Calculate the translation of the rotated pivot:
pivot_rotate = pivot.rotate(angle)
pivot_move = pivot_rotate - pivot
Finally calculate the origin of the rotated image:
origin = (pos[0] + min_box[0] - pivot_move[0], pos[1] - max_box[1] + pivot_move[1])
rotated_image = pygame.transform.rotate(image, angle)
screen.blit(rotated_image, origin)
If the image has to be additionally zoomed, then the zoom has to be taken into account when the origin of the image is calculated:
move = (-pivot[0] + min_box[0] - pivot_move[0], pivot[1] - max_box[1] + pivot_move[1])
origin = (pos[0] + zoom * move[0], pos[1] + zoom * move[1])
rotozoom_image = pygame.transform.rotozoom(image, angle, zoom)
screen.blit(rotozoom_image, origin)
In the following example program, the function blitRotate
does all the above steps and "blit" a rotated image to a surface. pos
is the position of the image. originPos
is the point on the image which is placed on pos
and the pivot.
Minimal example: repl.it/@Rabbid76/PyGame-RotateAroundPivotAndZoom
import pygame
pygame.init()
screen = pygame.display.set_mode((300, 300))
clock = pygame.time.Clock()
def blitRotate(surf, image, pos, originPos, angle, zoom):
# calcaulate the axis aligned bounding box of the rotated image
w, h = image.get_size()
box = [pygame.math.Vector2(p) for p in [(0, 0), (w, 0), (w, -h), (0, -h)]]
box_rotate = [p.rotate(angle) for p in box]
min_box = (min(box_rotate, key=lambda p: p[0])[0], min(box_rotate, key=lambda p: p[1])[1])
max_box = (max(box_rotate, key=lambda p: p[0])[0], max(box_rotate, key=lambda p: p[1])[1])
# calculate the translation of the pivot
pivot = pygame.math.Vector2(originPos[0], -originPos[1])
pivot_rotate = pivot.rotate(angle)
pivot_move = pivot_rotate - pivot
# calculate the upper left origin of the rotated image
move = (-originPos[0] + min_box[0] - pivot_move[0], -originPos[1] - max_box[1] + pivot_move[1])
origin = (pos[0] + zoom * move[0], pos[1] + zoom * move[1])
# get a rotated image
rotozoom_image = pygame.transform.rotozoom(image, angle, zoom)
# rotate and blit the image
surf.blit(rotozoom_image, origin)
# draw rectangle around the image
pygame.draw.rect (surf, (255, 0, 0), (*origin, *rotozoom_image.get_size()),2)
try:
image = pygame.image.load('AirPlaneFront1-128.png')
except:
text = pygame.font.SysFont('Times New Roman', 50).render('image', False, (255, 255, 0))
image = pygame.Surface((text.get_width()+1, text.get_height()+1))
pygame.draw.rect(image, (0, 0, 255), (1, 1, *text.get_size()))
image.blit(text, (1, 1))
w, h = image.get_size()
start = False
angle, zoom = 0, 1
done = False
while not done:
clock.tick(60)
for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True
elif event.type == pygame.KEYDOWN or event.type == pygame.MOUSEBUTTONDOWN:
start = True
pos = (screen.get_width()/2, screen.get_height()/2)
screen.fill(0)
blitRotate(screen, image, pos, (w/2, h/2), angle, zoom)
if start:
angle += 1
zoom += 0.01
if zoom > 5:
zoom = 1
pygame.draw.line(screen, (0, 255, 0), (pos[0]-20, pos[1]), (pos[0]+20, pos[1]), 3)
pygame.draw.line(screen, (0, 255, 0), (pos[0], pos[1]-20), (pos[0], pos[1]+20), 3)
pygame.draw.circle(screen, (0, 255, 0), pos, 7, 0)
pygame.display.flip()
pygame.quit()
exit()
How can you rotate an image around an off center pivot in Pygame
First the position of the pivot on the Surface
has to be defined:
image = pygame.image.load("boomerang64.png") # 64x64 surface
pivot = (48, 21) # position of the pivot on the image
When an image is rotated, then its size increase. We have to compare the axis aligned bounding box of the image before the rotation and after the rotation.
For the following math pygame.math.Vector2
is used. Note in screen coordinates the y points down the screen, but the mathematical y axis points form the bottom to the top. This causes that the y axis has to be "flipped" during calculations. Notice that pygame.math.Vector2.rotate
rotates in the opposite direction than pygame.transform.rotate
. Therefore the angle has to be inverted.
Set up a list with the 4 corner points of the bounding box and rotate the vectors to the corner points by pygame.math.Vector2.rotate
. Finally find the minimum of the rotated box. Since the y axis in pygame points downwards, this has to be compensated by finding the maximum of the rotated inverted height ("max(rotate(-h))"):
Compute the vector from the center of the image to the pivot:
image_rect = image.get_rect(topleft = (pos[0] - originPos[0], pos[1]-originPos[1]))
offset_center_to_pivot = pygame.math.Vector2(pos) - image_rect.center
Rotate the offset vector:
rotated_offset = offset_center_to_pivot.rotate(-angle)
Calculate the center of the rotated image:
rotated_image_center = (pos[0] - rotated_offset.x, pos[1] - rotated_offset.y)
Rotate and blit the image:
rotated_image = pygame.transform.rotate(image, angle)
rotated_image_rect = rotated_image.get_rect(center = rotated_image_center)
screen.blit(rotated_image, rotated_image_rect)
In the following example program, the function blitRotate(surf, image, pos, originPos, angle)
does all the above steps and blit
a rotated image to the Surface which is associated to the display:
surf
is the target Surfaceimage
is the Surface which has to be rotated andblit
pos
is the position of the pivot on the target Surfacesurf
(relative to the top left ofsurf
)originPos
is position of the pivot on theimage
Surface (relative to the top left ofimage
)angle
is the angle of rotation in degrees
import math
import pygame
def blitRotate(surf, image, pos, originPos, angle):
image_rect = image.get_rect(topleft = (pos[0] - originPos[0], pos[1]-originPos[1]))
offset_center_to_pivot = pygame.math.Vector2(pos) - image_rect.center
rotated_offset = offset_center_to_pivot.rotate(-angle)
rotated_image_center = (pos[0] - rotated_offset.x, pos[1] - rotated_offset.y)
rotated_image = pygame.transform.rotate(image, angle)
rotated_image_rect = rotated_image.get_rect(center = rotated_image_center)
surf.blit(rotated_image, rotated_image_rect)
pygame.init()
size = (400,400)
screen = pygame.display.set_mode(size)
clock = pygame.time.Clock()
image = pygame.image.load('Boomerang64.png')
pivot = (48, 21)
angle, frame = 0, 0
done = False
while not done:
clock.tick(60)
for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True
screen.fill(0)
pos = (200 + math.cos(frame * 0.05)*100, 200 + math.sin(frame * 0.05)*50)
blitRotate(screen, image, pos, pivot, angle)
pygame.draw.line(screen, (0, 255, 0), (pos[0]-20, pos[1]), (pos[0]+20, pos[1]), 3)
pygame.draw.line(screen, (0, 255, 0), (pos[0], pos[1]-20), (pos[0], pos[1]+20), 3)
pygame.draw.circle(screen, (0, 255, 0), pos, 7, 0)
pygame.display.flip()
frame += 1
angle += 10
pygame.quit()
exit()
The same algorithm can be used for a Sprite, too.
In that case the position (self.pos
), pivot (self.pivot
) and angle (self.angle
) are instance attributes of the class.
In the update
method the self.rect
and self.image
attributes are computed.
Minimal example: repl.it/@Rabbid76/PyGame-RotateSpriteAroundOffCenterPivot
import math
import pygame
class SpriteRotate(pygame.sprite.Sprite):
def __init__(self, imageName, origin, pivot):
super().__init__()
self.image = pygame.image.load(imageName)
self.original_image = self.image
self.rect = self.image.get_rect(topleft = (origin[0]-pivot[0], origin[1]-pivot[1]))
self.origin = origin
self.pivot = pivot
self.angle = 0
def update(self):
# offset from pivot to center
image_rect = self.original_image.get_rect(topleft = (self.origin[0] - self.pivot[0], self.origin[1]-self.pivot[1]))
offset_center_to_pivot = pygame.math.Vector2(self.origin) - image_rect.center
# roatated offset from pivot to center
rotated_offset = offset_center_to_pivot.rotate(-self.angle)
# roatetd image center
rotated_image_center = (self.pos[0] - rotated_offset.x, self.pos[1] - rotated_offset.y)
# get a rotated image
self.image = pygame.transform.rotate(self.original_image, self.angle)
self.rect = self.image.get_rect(center = rotated_image_center)
self.angle += 10
pygame.init()
size = (400,400)
screen = pygame.display.set_mode(size)
clock = pygame.time.Clock()
boomerang = SpriteRotate('Boomerang64.png', (200, 200), (48, 21))
all_sprites = pygame.sprite.Group(boomerang)
frame = 0
done = False
while not done:
clock.tick(60)
for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True
pos = (200 + math.cos(frame * 0.05)*100, 200 + math.sin(frame * 0.05)*50)
boomerang.pos = pos
all_sprites.update()
screen.fill(0)
all_sprites.draw(screen)
#pygame.draw.line(screen, (0, 255, 0), (pos[0]-20, pos[1]), (pos[0]+20, pos[1]), 3)
#pygame.draw.line(screen, (0, 255, 0), (pos[0], pos[1]-20), (pos[0], pos[1]+20), 3)
#pygame.draw.circle(screen, (0, 255, 0), pos, 7, 0)
pygame.display.flip()
frame += 1
pygame.quit()
exit()
How do I rotate an image around its center using Pygame?
How to rotate an image around its center while its scale is getting larger(in Pygame)
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