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Quiz: Ellipse & Polygon Drawing

Test your understanding of the two methods — ellipse() and poly() — that draw nearly every curved and angled feature on a robot's face.

1. Why does FrameBuf have no separate method for drawing a circle?

  1. Because a circle is simply an ellipse whose xradius and yradius are equal
  2. Because circles must be built from many small fb.poly() segments instead
  3. Because circles cannot be drawn on a rectangular display
  4. Because fb.rect() with rounded corners already produces a circle
Show Answer

The correct answer is A. An ellipse is controlled by two independent radii, one for width and one for height, and it becomes a perfectly round circle whenever those two values match. A single method therefore covers wide ovals, tall ovals, and circles — which is why fb.ellipse(108, 40, 10, 10, WHITE) draws a circle with no special syntax.

Concept Tested: Circle As Special Ellipse

See: A Circle Is Just a Special Ellipse

2. You want to draw only the left half of an eye — the upper-left and lower-left quadrants. What quadrant fill code do you pass?

  1. 3
  2. 9
  3. 12
  4. 6
Show Answer

The correct answer is D. Upper left has bit value 2 and lower left has bit value 4, so the mask is 2 + 4 = 6. Option A (3) is the top half, option C (12) is the bottom half, and option B (9) is the right side. Because the bit values are tied to fixed screen quadrants, always check each value against its actual position rather than guessing which numbers mean "left."

Concept Tested: Quadrant Fill Code

See: The Real Trick: Quadrant Fill Code

3. How does fb.ellipse() interpret its first two arguments, compared with fb.rect()?

  1. Both treat them as the top-left corner of the shape
  2. fb.ellipse() treats them as the shape's center; fb.rect() treats them as its top-left corner
  3. fb.ellipse() treats them as the top-left corner; fb.rect() treats them as its center
  4. Both treat them as the center of the shape
Show Answer

The correct answer is B. An ellipse is positioned by its center point, while a rectangle is positioned by its top-left corner. The difference makes sense in practice: eyes and pupils are naturally described by where their middle sits, since a curved shape has no meaningful corner to measure from.

Concept Tested: Ellipse Method

See: Drawing Curves: The Ellipse Method

4. A student's curved eyebrow looks jagged and staircase-like along its edge. What should they do?

  1. Increase both radii so the curve has more pixels to work with
  2. Redraw the curve with fb.poly(), which produces smooth edges
  3. Nothing — every pixel is fully on or off, so some blockiness is expected at this resolution
  4. Enable the anti-aliasing argument in the fb.ellipse() call
Show Answer

The correct answer is C. The anti-aliasing limitation means these frame buffers cannot blend a pixel partway between two colors to soften an edge. Blockiness is how the hardware works, not a bug in the code, and there is no anti-aliasing argument to enable. Viewed from conversational distance — where a person would actually stand — the curve reads as smooth anyway.

Concept Tested: Anti-Aliasing Limitation

See: Why Curves Look a Little Blocky

5. Which quadrant fill code produces a smiling mouth curve — the bottom half of a wide, flat ellipse?

  1. 12
  2. 3
  3. 15
  4. 5
Show Answer

The correct answer is A. The bottom half combines lower left (4) and lower right (8), giving 12. Option B (3) is the top half, which would read as a frown or a drooping eyelid instead, and option C (15) is the full ellipse drawn by default when the mask is omitted entirely.

Concept Tested: Quadrant Fill Code

See: The Real Trick: Quadrant Fill Code

6. What is a point array?

  1. A dictionary mapping vertex names to their coordinates
  2. A list of (x, y) tuples, one per corner of a polygon
  3. A flat array of alternating x and y values describing every corner of a polygon in order
  4. An array holding one entry per pixel the polygon will light up
Show Answer

The correct answer is C. fb.poly() expects all coordinates packed into one flat sequence — x1, y1, x2, y2, x3, y3 — not separate pairs. MicroPython builds these with array('B', [...]), where 'B' stores each number as an unsigned byte from 0 to 255, which is ample for screen coordinates and far more memory-efficient than a general-purpose list.

Concept Tested: Point Array

See: Points in a List: The Point Array

7. A triangle's point array lists three vertices. Why does the drawn shape still show three connected edges?

  1. Because fb.poly() silently adds a fourth vertex at the shape's center
  2. Because the fill=True argument closes any gap in the outline
  3. Because the array module repeats the first coordinate pair automatically
  4. Because fb.poly() always draws a closing line from the last vertex back to the first
Show Answer

The correct answer is D. The closed polygon path behavior means you never repeat the starting coordinate at the end of the array. A hexagon needs only six vertex pairs, not seven, even though the finished shape has six visible edges — which saves both typing and memory.

Concept Tested: Closed Polygon Path

See: Never Repeat the Start: Closed Polygon Path

8. Why does a triangle eyebrow express emotion more effectively than the rectangle eyebrow from Chapter 6?

  1. A triangle uses fewer drawing calls, so it can be redrawn more often
  2. A triangle can slant, so reordering just three vertices changes the eyebrow's emotional read
  3. A triangle is a concave polygon, and concave shapes read as more dynamic
  4. A triangle can be filled while a rectangle can only be outlined
Show Answer

The correct answer is B. A flat rectangular bar communicates "eyebrow" but stays neutral. Because a triangle's three vertices can be arranged to slant sharply inward or outward, the same method with a different point array turns a calm brow into a furrowed, angry one. Both shapes can be filled, and a triangle is convex, which rules out options C and D.

Concept Tested: Triangle Eyebrow Shape

See: A Concrete Example: Triangle Eyebrow Shape

9. When should a designer reach for fb.poly() with many closely spaced vertices instead of fb.ellipse()?

  1. Whenever a shape needs to be filled rather than outlined
  2. Whenever a shape must be drawn faster than an ellipse allows
  3. When the design calls for an irregular curve that a regular oval cannot produce
  4. When the shape must stay entirely within one quadrant of the screen
Show Answer

The correct answer is C. fb.ellipse() is fast and simple, but it only ever draws a regular oval. Approximating curves with lines — computing many points along an arc and packing them into a point array — takes over exactly where a regular ellipse cannot reach, such as an eyebrow arched into a specific irregular sweep. Many small segments are visually indistinguishable from a true curve at this resolution.

Concept Tested: Approximating Curves With Lines

See: Approximating Curves With Lines

10. What is the effect of these two consecutive calls: fb.ellipse(40, 30, 10, 10, WHITE, True, 15) followed by fb.ellipse(40, 30, 10, 10, BLACK, True, 3)?

  1. A circle whose top half is erased, producing a drooping, half-closed eye
  2. A circle whose bottom half is erased, producing a wide, startled eye
  3. Two overlapping circles, one white and one black, side by side
  4. Nothing visible, because the second call erases the entire first circle
Show Answer

The correct answer is A. The first call draws a full white circle (mask 15). The second redraws the same circle in the background color with mask 3 — upper right plus upper left — erasing only the top half. Because later draw calls paint over earlier ones, the result is a lowered eyelid. Mask 3 covers just two of four quadrants, which rules out option D.

Concept Tested: Quadrant Fill Code

See: Putting It Together: An Eye, an Eyelid, and an Eyebrow