#fill_premul

1fn fill_premul(inout self, color: vec4) -> vec4

The fill_premul function fills the current shape in the Sdf2d drawing context with a pre-multiplied RGBA color. It blends the provided color with the existing content and resets the internal shape and clipping parameters, preparing the context for subsequent drawing operations.

#Parameters

• self (inout): A reference to the Sdf2d instance where the fill operation is performed. The function modifies the result, shape, old_shape, clip, and has_clip fields of self in place.
• color (vec4): A pre-multiplied RGBA color used to fill the shape.

#Returns

• vec4: The updated result color after the fill operation, reflecting the blended color of the input and the existing content. The shape and clipping parameters are reset after this operation.

#Example

1fn pixel(self) -> vec4 {
2    // Create an Sdf2d drawing context for the current viewport.
3    let sdf = Sdf2d::viewport(self.pos * self.rect_size);
4
5    // Draw a rectangle with rounded corners.
6    sdf.box(10.0, 10.0, 80.0, 80.0, 5.0);
7
8    // Apply a semi-transparent red fill using pre-multiplied alpha.
9    // The RGB components are multiplied by the alpha (0.5).
10    sdf.fill_premul(vec4(1.0 * 0.5, 0.0 * 0.5, 0.0 * 0.5, 0.5));
11
12    // Rotate the drawing by 45 degrees around the center of the rectangle.
13    sdf.rotate(PI * 0.25, 50.0, 50.0);
14
15    // Return the final color result.
16    return sdf.result;
17}

#Explanation

In this example:

• Create Drawing Context: Initialize the Sdf2d context using the current position (self.pos) scaled by self.rect_size, which represents the size of the viewport.
• Draw Shape: Use sdf.box to draw a rectangle starting at position (10.0, 10.0) with a width and height of 80.0 units and corner radius of 5.0.
• Apply Fill: Call fill_premul to fill the rectangle with a semi-transparent red color. Since fill_premul expects a pre-multiplied color, we multiply each RGB component by the alpha (0.5), resulting in vec4(0.5, 0.0, 0.0, 0.5).
• Reset State: After fill_premul, the shape and clipping parameters are reset, allowing you to start drawing new shapes without manually resetting the state.
• Rotate Drawing: Rotate the entire drawing context by 45 degrees (PI * 0.25 radians) around the point (50.0, 50.0), which is the center of the rectangle.
• Return Result: Return sdf.result, which contains the final rendered color after all drawing operations.

#Notes

• Pre-multiplied Alpha: Ensure that the color provided to fill_premul is pre-multiplied, meaning each RGB component is multiplied by the alpha component. This is crucial for correct blending and transparency effects.
• State Reset: Unlike fill_keep_premul, the fill_premul function resets the internal shape and clipping state after execution. This means you can define new shapes immediately after calling fill_premul without manual resets.
• Usage: Use fill_premul when you want to fill a shape and prepare the context for new drawing operations without preserving the current shape and clipping settings.
• Transformations: You can apply transformations such as rotate, translate, or scale to manipulate the drawing context as needed. In this example, rotate is used to rotate the entire drawing.

#Important Considerations

• Color Accuracy: When working with pre-multiplied alpha, it's essential to pre-multiply the RGB components to ensure accurate color blending.
• Alpha Blending: Pre-multiplied alpha helps in avoiding artifacts in blending, especially when rendering semi-transparent textures or layers.
• Subsequent Operations: Since fill_premul resets the shape and clipping state, any shapes drawn before calling it will not affect subsequent drawing operations. Plan your drawing sequence accordingly.