HTML Canvas Colors

The HTML5 <canvas> element allows you to use colors in various ways to fill shapes, outline paths, and add visual appeal to your graphics. In this tutorial, you’ll learn how to:

1. Apply solid colors for fills and strokes.
2. Use gradients for dynamic coloring.
3. Create patterns using images or existing canvas content.
4. Combine color techniques for advanced effects.

1. Setting Colors

The Canvas API uses two primary properties for colors:

• fillStyle: Sets the fill color for shapes.
• strokeStyle: Sets the color of the outlines (strokes).

Example 1: Solid Colors for Fill and Stroke

<canvas id="myCanvas" width="500" height="300" style="border: 1px solid black;"></canvas>
<script>
    const canvas = document.getElementById("myCanvas");
    const ctx = canvas.getContext("2d");

    // Fill with a solid color
    ctx.fillStyle = "blue";
    ctx.fillRect(50, 50, 150, 100);

    // Outline with a solid color
    ctx.strokeStyle = "red";
    ctx.lineWidth = 5;
    ctx.strokeRect(250, 50, 150, 100);
</script>

2. Using RGBA for Transparency

The RGBA color model adds an alpha channel for transparency.

Example 2: Applying RGBA Colors

// Transparent fill
ctx.fillStyle = "rgba(0, 255, 0, 0.5)"; // Green with 50% opacity
ctx.fillRect(50, 200, 150, 100);

// Transparent stroke
ctx.strokeStyle = "rgba(255, 0, 0, 0.8)"; // Red with 80% opacity
ctx.lineWidth = 4;
ctx.strokeRect(250, 200, 150, 100);

3. Linear Gradients

You can create smooth transitions between colors using linear gradients.

Syntax:

const gradient = ctx.createLinearGradient(x0, y0, x1, y1);
gradient.addColorStop(position, color);

Example 3: Linear Gradient Fill

const gradient = ctx.createLinearGradient(0, 0, 500, 0);
gradient.addColorStop(0, "blue");
gradient.addColorStop(0.5, "green");
gradient.addColorStop(1, "yellow");

ctx.fillStyle = gradient;
ctx.fillRect(50, 50, 400, 200);

Explanation:

• createLinearGradient(x0, y0, x1, y1): Creates a gradient from (x0, y0) to (x1, y1).
• addColorStop(position, color): Adds a color stop at the given position (0 to 1).

4. Radial Gradients

Radial gradients create color transitions radiating from a central point.

Syntax:

const gradient = ctx.createRadialGradient(x0, y0, r0, x1, y1, r1);
gradient.addColorStop(position, color);

Example 4: Radial Gradient Fill

const gradient = ctx.createRadialGradient(250, 150, 50, 250, 150, 150);
gradient.addColorStop(0, "red");
gradient.addColorStop(1, "purple");

ctx.fillStyle = gradient;
ctx.fillRect(50, 50, 400, 200);

Explanation:

• createRadialGradient(x0, y0, r0, x1, y1, r1):
  • (x0, y0, r0): Defines the inner circle.
  • (x1, y1, r1): Defines the outer circle.

5. Patterns

You can use images or existing canvas content to create repeating patterns.

Syntax:

const pattern = ctx.createPattern(image, repeat);
ctx.fillStyle = pattern;

Example 5: Using an Image Pattern

const image = new Image();
image.src = "https://via.placeholder.com/50"; // Use any image URL
image.onload = () => {
    const pattern = ctx.createPattern(image, "repeat"); // Options: repeat, repeat-x, repeat-y, no-repeat
    ctx.fillStyle = pattern;
    ctx.fillRect(50, 50, 400, 200);
};

6. Combining Colors

You can combine solid colors, gradients, and patterns to create complex effects.

Example 6: Combining Linear Gradient and Stroke

// Linear Gradient Fill
const gradient = ctx.createLinearGradient(0, 0, 500, 0);
gradient.addColorStop(0, "blue");
gradient.addColorStop(1, "cyan");
ctx.fillStyle = gradient;
ctx.fillRect(50, 50, 400, 200);

// Stroked Outline
ctx.strokeStyle = "red";
ctx.lineWidth = 10;
ctx.strokeRect(50, 50, 400, 200);

7. Practical Example: Sunset Scene

Example: Creating a Sunset Scene with Colors

// Sky (Linear Gradient)
const skyGradient = ctx.createLinearGradient(0, 0, 0, 300);
skyGradient.addColorStop(0, "orange");
skyGradient.addColorStop(1, "blue");
ctx.fillStyle = skyGradient;
ctx.fillRect(0, 0, 500, 300);

// Sun (Radial Gradient)
const sunGradient = ctx.createRadialGradient(250, 150, 20, 250, 150, 100);
sunGradient.addColorStop(0, "yellow");
sunGradient.addColorStop(1, "transparent");
ctx.fillStyle = sunGradient;
ctx.beginPath();
ctx.arc(250, 150, 100, 0, Math.PI * 2);
ctx.fill();

// Ocean
ctx.fillStyle = "darkblue";
ctx.fillRect(0, 250, 500, 50);

8. Best Practices

1. Reset Colors as Needed:
   • fillStyle and strokeStyle persist until changed.
2. Use Gradients for Smooth Transitions:
   • Avoid overusing solid colors for large areas.
3. Combine Techniques:
   • Mix solid colors, gradients, and patterns for complex visuals.
4. Optimize Patterns:
   • Use optimized or small images for patterns to improve performance.

9. Browser Support

10. Conclusion

In this tutorial, you learned:

1. How to set colors using fillStyle and strokeStyle.
2. How to create and apply linear and radial gradients.
3. How to use patterns for fills.
4. How to combine multiple color techniques for advanced effects.