使用Pyxel开发2D游戏：如何绕原点旋转图像？

Hey there! Great question—rotating sprites in Pyxel does require a bit of extra legwork since pyxel.blt doesn’t support rotation directly out of the box. Let me break down how to implement this step by step.

The Core Idea: Rotation Math #

To rotate a sprite around a pivot point (like its center or top-left corner), you’ll use basic trigonometry with a rotation matrix. For any point (rel_x, rel_y) relative to the pivot, rotating it by θ radians gives you a new point:

• rotated_x = rel_x * cosθ - rel_y * sinθ
• rotated_y = rel_x * sinθ + rel_y * cosθ

We’ll apply this to every pixel in your sprite to draw it in the rotated position.

Custom Rotated Blit Function #

Here’s a reusable function that mimics pyxel.blt but adds rotation support. It calculates each pixel’s rotated position and draws it to the screen:

import math

def rotated_blt(screen_x, screen_y, img_bank, u, v, width, height, angle, pivot_x=0, pivot_y=0):
    # Calculate the pivot's position within the source sprite
    pivot_u = u + pivot_x
    pivot_v = v + pivot_y

    # Iterate over every pixel in the sprite
    for dy in range(height):
        for dx in range(width):
            # Get the pixel's position relative to the pivot
            rel_x = dx - pivot_x
            rel_y = dy - pivot_y

            # Apply rotation matrix (convert angle to radians first if needed)
            cos_theta = math.cos(angle)
            sin_theta = math.sin(angle)
            new_rel_x = rel_x * cos_theta - rel_y * sin_theta
            new_rel_y = rel_x * sin_theta + rel_y * cos_theta

            # Calculate final screen position
            final_x = screen_x + new_rel_x + pivot_x
            final_y = screen_y + new_rel_y + pivot_y

            # Get the pixel color from the source image
            pixel_color = pyxel.image(img_bank).get(u + dx, v + dy)

            # Draw only non-transparent pixels (assuming color 0 is transparent)
            if pixel_color != 0:
                pyxel.pset(int(final_x), int(final_y), pixel_color)

How to Use It #

Let’s say you have a 16x16 sprite in image bank 0, starting at (0,0) in the image. To draw it at screen position (100,100) rotated 45 degrees around its center:

# Convert 45 degrees to radians
rotation_angle = math.radians(45)
# Pivot is the center of the 16x16 sprite
rotated_blt(100, 100, 0, 0, 0, 16, 16, rotation_angle, pivot_x=8, pivot_y=8)

Performance Tips #

• For small sprites (16x16 or smaller), the above function works perfectly for most small games.
• If you need to rotate sprites frequently (like a spinning player character), pre-render rotated versions of the sprite into unused image banks during initialization. Then you can use regular pyxel.blt to draw them, which is much faster than calculating pixels in real-time.

内容的提问来源于stack exchange，提问作者F. Leone