python - Shifting the color value based on percentage from green to red using PyGame

Question

I'm trying to make a health bar that scales the colors of GREEN to RED depending on the percentage of health. Basically, i'm trying to make the value of 0.5 correspond to (255, 255, 0), and a value of 1.0 correspond to (0, 255, 0) and a value of 0.0 correspond to (255,0,0). I saw This Post, which has the same intent as I, but doesn't quite help code-wise. Same applies f?r This Post.

This is my current code:

def draw_player_health_mana(surface, x, y, curr_value, start_value, type_bar, font):
        #TRANSFORMS THE VALUES TO PERCENTAGE
        pct = curr_value/start_value
     
        if pct < 0:
            pct = 0
        #SIZE OF THE HEALTH BAR
        BAR_LENGTH = 150
        BAR_HEIGHT = 18
        
        #INITIAL COLOR VALUES
        red_color = 255
        green_color = 255
        
        #THE FILLED BAR TO DISPLAY VISUALLY OF CURRENT HP COMPARED TO MAX HP
        fill = pct * BAR_LENGTH
        
        #PYGAME RECTANGLES
        outline_rect = pg.Rect(x, y, BAR_LENGTH, BAR_HEIGHT)
        fill_rect = pg.Rect(x, y, fill, BAR_HEIGHT)

        #CHECKS WHAT TYPE OF BAR IS CALLED FOR - THERES MANA AND HEALTH
        if type_bar == 'health':
            #THE DIFFERENCE IN PERCENTAGE, MEANT AS AN INCREASE
            pct_diff = 1.0 - pct
            
            #INTENT IS TO CHECK IF PERCENTAGE IS ABOVE 50%, THEN DECREASE THE GREEN SPECTRUM
            #BUT AS SHOWN, IT NEVER DECREASES TO 0, BUT ONLY TO HALF OF 255...
            #LIKEWISE FOR THE INCREASE OF RED_COLOR 
            if pct > 0.5: 
                red_color = 255 * pct       #### Can't really figure out how to deal with this part 
            else:                                   
                green_color = 255*pct_diff
            
            col = (red_color, green_color, 0)
            print(col)
        elif type_bar == 'mana':
            col = BLUE

        pg.draw.rect(surface, col, fill_rect)
        pg.draw.rect(surface, BLACK, outline_rect, 2)
        
        text = font.render(str(curr_value) + "/" + str(start_value), True, BLACK)
        text_rect = text.get_rect(center=(BAR_LENGTH/2 + x, BAR_HEIGHT/2 + y))
        surface.blit(text, text_rect)

As commented in the syntax above, the issue is the color conversion. Color works as (RED, GREEN, BLUE). For a nice green color of having full health, it should be (0, 255, 0). However, as the health shifts towards 50%, the red color must reach the value of 255 (Causing for (255, 255, 0), which i cannot figure out how to effectively do whilst transitioning the decrease in green to 0 to reach a more of a red color.. I feel really lost on this matter, and any type of help would be greatly appreciated.

Thanks in advance.

question from:https://stackoverflow.com/questions/65904437/shifting-the-color-value-based-on-percentage-from-green-to-red-using-pygame

Answer 1

0.5 correspond to (255, 255, 0), and a value of 1.0 correspond to (0, 255, 0) (255, 255, 0), and a value of 1.0 correspond to (0, 255, 0)

Therefore the green color component is min(255, pct_diff*2 * 255) and the red color component is min(255, pct*2 * 255):

pct_diff = 1.0 - pct
red_color = min(255, pct_diff*2 * 255)
green_color = min(255, pct*2 * 255)
col = (red_color, green_color, 0)