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Bubbly

Bubbly. David Doty and Mark Fielbig. What is Bubbly?. Bubbly is an interface proposed for creating 3D models out of 2D strokes. Bubbly uses only OpenGL, GLUT, and the C++ STL. We were inspired by Teddy a 1999 paper in the ACM SIGGRAPH by Igarashi, Matsuoka, and Tanaka.

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Bubbly

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  1. Bubbly David Doty and Mark Fielbig Stony Brook University

  2. What is Bubbly? • Bubbly is an interface proposed for creating 3D models out of 2D strokes. • Bubbly uses only OpenGL, GLUT, and the C++ STL. • We were inspired by Teddy a 1999 paper in the ACM SIGGRAPH by Igarashi, Matsuoka, and Tanaka. Stony Brook University

  3. What Can Bubbly Do? • Bubbly supports five operations: • Model Initialization • Model Cutting • Model Addition • Camera Rotation • Camera Zooming • The desired model is “sculpted” by the user through the combination of these operations. Stony Brook University

  4. Interaction With Bubbly • The user is initially presented with a 2D triangle grid to draw on. The user clicks and drags the mouse in order to draw the silhouette of the desired model. • The user then right clicks inside of the silhouette to transform the 2D input stroke to a 3D model. This is what we call inflation. Stony Brook University

  5. Interaction With Bubbly • After the user is presented with the 3D model Bubbly’s camera operations become available. • Rotation around the model’s bounding volume can be achieved by left clicking and dragging. The model will rotate in the direction the mouse is dragged. • The camera can be zoomed in and out using the mouse wheel or the up and down arrow keys. Stony Brook University

  6. Interaction With Bubbly • In addition to camera controls the model can be manipulated with the mouse. • To cut the model the user right clicks and drags across it. • The user combines camera rotation and cutting to project the cutting stroke into the scene and dispose of the smaller portion of the model. Stony Brook University

  7. Interaction With Bubbly • The user can return to creation mode by pressing the middle mouse button or the ‘A’ key.This will repeat the initialization process allowing addition to the model. • The user can press the ‘R’ key to return to creation mode and dispose of the existing model. Stony Brook University

  8. Bubbly’s Algorithms • Input Stroke Creation • To create the input stroke differential line segments are inserted as the mouse is moved along the screen. • The distance formula is used to determine when a new line segment should be added. • When the user releases the mouse the input stroke is closed and then checked for self intersection. • If the stroke is accepted: • The bounding box is computed • The stroke is intersected with the grid Stony Brook University

  9. Bubbly’s Algorithms • Silhouette Filling • At this point the bordering triangles are known but the interior triangles aren’t. • A “seed” is planted within the bordering triangles and a modified flood-fill algorithm is used to determine the interior triangles. • Inflation • The inflation process consists of three steps: • Every vertex has its east most, west most, north most, and south most “fringe vertices” calculated. • Each vertex gets a z value based on its distance away from its fringe vertices. • The second half of the model is mirrored on the opposite side by copying each point and negating its z value. Stony Brook University

  10. Bubbly’s Algorithms • Determining Fringe Vertices • The mesh is traversed in each cardinal direction until a gap is encountered. • Elevating Vertices • Each vertex is then elevated according to a modified circle equation. Stony Brook University

  11. Bubbly’s Algorithms • Mirroring the Model • At this point there is only half a model, the second half is created. • This Completes the Inflation Process Stony Brook University

  12. Bubbly’s Algorithms • Camera Movement • The camera rotates along spherical coordinates. The coordinates are calculated with the following equations: • Mouse movement in the x-axis changes , the y-axis changes . • Zooming in is accomplished by decreasing the value of and zooming out is accomplished by increasing the value of . Stony Brook University

  13. Bubbly’s Algorithms • Model Cutting • Cutting is achieved by projecting the cut stroke to the near and far plane to create an intersection plane. • For every vertex in the mesh a vector is drawn from an arbitrary point on the plane to that vertex. Call this vector . The plane normal, , is then dotted with . • The sign of the dot product tells what side of the plane that vertex lies on. • A count of triangles on each side is recorded and the side with the lower count is removed from the model mesh. Stony Brook University

  14. Bubbly In Action! Stony Brook University

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