Blender Donut Tutorial: Adding Sprinkles with Geometry Nodes

Introduction

• Geometry Nodes is accessed via the tab on the top of the screen.
• Adjusts the screen layout; close unnecessary parts like the spreadsheet view.

Creating and Applying Geometry Nodes

• Select icing and click the 'New' button to add a Geometry Nodes modifier.
• Geometry Nodes allows for flexible modifications post-object creation.
• Node-based system similar to material nodes but serves different functions.

How Geometry Nodes Work

• Geometry nodes process input mesh and output the modified mesh.
• Example: Using a set position node to demonstrate how geometry nodes can raise parts without directly altering the mesh.
• Modifications via geometry nodes are highly flexible and can be made to parameters visible in the modifier stack.

Adding Sprinkles

1. Scattering Points on Icing:

   • Use Shift + A > Point distribute points on faces to scatter points.
   • Initially, the mesh will disappear because only points are being rendered.
   • Use Shift + A > Geometry > Join Geometry to add back the original mesh while keeping the points.

2. Creating a Sprinkle Object:

   • Add a low poly sphere (Shift + A > Mesh > UV Sphere) to serve as sprinkles.
   • Adjust segments and rings to lower values to maintain performance.
   • Scale the sphere down (0.1 in this case).

3. Using Points for Sprinkles:

   • Drag the sphere from outliner to Geometry Nodes editor.
   • Use Shift + A > Instances > Instances on points to replace scattered points with the sphere.
   • Adjust density appropriately.

4. Avoid Overlapping Sprinkles:

   • Change distribution to Poisson Disc in Point distribute node.
   • Adjust distance min to avoid overlap but maintain a natural look.

Weight Painting for Controlled Sprinkle Placement

• Set up weight painting for the icing object.
• Paint the desired sprinkle density in the weight paint mode.
• Name the vertex group created by weight painting (e.g., 'sprinkle_density').
• Reference this vertex group in the Geometry Nodes as a named attribute to control sprinkle distribution.

Adjusting Sprinkle Positions and Density

• Utilize control and paint to refine sprinkle placement manually for realistic effects.
• Pin Geometry Nodes window to maintain visibility.
• Expose density parameter to the modifier stack for easy editing.

Rescaling the Donut

• Realistically scale donut size (suggested 1:10 scale for a 12cm donut).
• Apply scale transformations globally to avoid inconsistencies.

Applying Scale and Adjusting Density Accordingly

• Correct the overall density and minimum distance for scattered sprinkles post-scaling.
• Consider adding a math node to help maintain a manageable interface by multiplying values within Geometry Nodes.

Conclusion

• This tutorial has set up sprinkles with correct scaling and density.
• Next steps include adding different types of sprinkles and adjusting rotations and colors.

Additional Tips

• Shift + A for adding nodes and objects.
• Use Numpad period or tilde key for quick object focusing.
• Employ weight painting creatively to simulate real-world randomness and imperfections.