围绕枢轴旋转和缩放图像，同时在 Pygame 中分别缩放宽度和高度

Question

我在一个列表中有一组关键帧，如下所示：

   [{
        "duration" : 20,
        "position" : [0,0],
        "scale" : [1, 1],
        "angle" : 0,
        "rgba" : [255,255,255,255]
    },
    {
        "duration" : 5,
        "position" : [0,0],
        "scale" : [1, 1.5],
        "angle" : 50,
        "rgba" : [255,255,255,255]
    }]

这个想法是能够在每一帧进行相应的转换。请注意，比例在宽度和高度之间是分开的。
问题来自尝试独立缩放宽度和高度，同时仍围绕枢轴旋转。

我尝试修改以下代码：(How to rotate an image around its center while its scale is getting larger(in Pygame))

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)

但我正在努力思考使其工作所必需的数学，我尝试将 zoom 分离成一个骗子，然后不是做 rotozoom ，而是先用 transform.scale 缩放，然后用 transform.rotate之后，但这也没有用。

为了更好地说明我的意思，应该是这样的：

它改变了它的宽度和高度，但枢轴保持不变

Answer 1

我建议采用此处介绍的稍微不同的方法：How to set the pivot point (center of rotation) for pygame.transform.rotate()?

调整此算法所需要做的就是通过缩放因子将矢量从图像中心缩放到图像上的轴心点：

offset_center_to_pivot = pygame.math.Vector2(origin) - image_rect.center

offset_center_to_pivot = (pygame.math.Vector2(origin) - image_rect.center) * scale

围绕枢轴点旋转图像、缩放和blits 图像的最终函数可能如下所示：

def blitRotate(surf, original_image, origin, pivot, angle, scale):

    image_rect = original_image.get_rect(topleft = (origin[0] - pivot[0], origin[1]-pivot[1]))
    offset_center_to_pivot = (pygame.math.Vector2(origin) - image_rect.center) * scale
    rotated_offset = offset_center_to_pivot.rotate(-angle)
    rotated_image_center = (origin[0] - rotated_offset.x, origin[1] - rotated_offset.y)
    rotozoom_image = pygame.transform.rotozoom(original_image, angle, scale)
    rect = rotozoom_image.get_rect(center = rotated_image_center)

    surf.blit(rotozoom_image, rect)

也可以分别为 x 和 y 轴指定缩放因子：

def blitRotate(surf, original_image, origin, pivot, angle, scale_x, scale_y):

    image_rect = original_image.get_rect(topleft = (origin[0] - pivot[0], origin[1]-pivot[1]))
    offset_center_to_pivot = pygame.math.Vector2(origin) - image_rect.center
    offset_center_to_pivot.x *= scale_x
    offset_center_to_pivot.y *= scale_y
    rotated_offset = offset_center_to_pivot.rotate(-angle)
    rotated_image_center = (origin[0] - rotated_offset.x, origin[1] - rotated_offset.y)
    scaled_image = pygame.transform.smoothscale(original_image, (image_rect.width * scale_x, image_rect.height * scale_y))
    rotozoom_image = pygame.transform.rotate(scaled_image, angle)
    rect = rotozoom_image.get_rect(center = rotated_image_center)

    surf.blit(rotozoom_image, rect)

另见Rotate surface

---

最小示例： repl.it/@Rabbid76/PyGame-RotateZoomPivot

import pygame

pygame.init()
screen = pygame.display.set_mode((500, 500))
clock = pygame.time.Clock()

def blitRotate(surf, original_image, origin, pivot, angle, scale):

    image_rect = original_image.get_rect(topleft = (origin[0] - pivot[0], origin[1]-pivot[1]))
    offset_center_to_pivot = (pygame.math.Vector2(origin) - image_rect.center) * scale
    rotated_offset = offset_center_to_pivot.rotate(-angle)
    rotated_image_center = (origin[0] - rotated_offset.x, origin[1] - rotated_offset.y)
    rotozoom_image = pygame.transform.rotozoom(original_image, angle, scale)
    rect = rotozoom_image.get_rect(center = rotated_image_center)

    surf.blit(rotozoom_image, rect)
    pygame.draw.rect (surf, (255, 0, 0), rect, 2)

try:
    image = pygame.image.load('AirPlane.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()

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

    pos = (screen.get_width()/2, screen.get_height()/2)
    
    screen.fill(0)
    blitRotate(screen, image, pos, (w/4, h/2), angle, zoom)
    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()

---

示例 2： repl.it/@Rabbid76/PyGame-RotateZoomPivot

import pygame

pygame.init()
screen = pygame.display.set_mode((400, 300))
clock = pygame.time.Clock()

def blitRotateZoomXY(surf, original_image, origin, pivot, angle, scale_x, scale_y):

    image_rect = original_image.get_rect(topleft = (origin[0] - pivot[0], origin[1]-pivot[1]))
    offset_center_to_pivot = pygame.math.Vector2(origin) - image_rect.center
    offset_center_to_pivot.x *= scale_x
    offset_center_to_pivot.y *= scale_y
    rotated_offset = offset_center_to_pivot.rotate(-angle)
    rotated_image_center = (origin[0] - rotated_offset.x, origin[1] - rotated_offset.y)
    scaled_image = pygame.transform.smoothscale(original_image, (image_rect.width * scale_x, image_rect.height * scale_y))
    rotozoom_image = pygame.transform.rotate(scaled_image, angle)
    rect = rotozoom_image.get_rect(center = rotated_image_center)

    surf.blit(rotozoom_image, rect)

cannon = pygame.image.load('icon/cannon.png')
cannon_mount = pygame.image.load('icon/cannon_mount.png')

angle, zoom_x, zoom_y = -90, 1, 1
stage = 0
done = False
while not done:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done = True

    pos = (screen.get_width()/3, screen.get_height()*3/4)
    
    screen.fill((192, 192, 192))
    blitRotateZoomXY(screen, cannon, pos, (33.5, 120), angle, zoom_x, zoom_y)
    screen.blit(cannon_mount, (pos[0]-43, pos[1]-16))
    pygame.display.flip()

    if stage == 0:
        angle += 1
        if angle >= -30:
            stage += 1
    elif stage == 1:
        zoom_y -= 0.05
        if zoom_y <= 0.7:
           stage += 1
    elif stage == 2: 
        zoom_y += 0.05
        if zoom_y >= 1:
           stage += 1
    elif stage == 3:
        angle -= 1
        if angle <= -90:
            stage = 0
    
pygame.quit()
exit()