Mandelbrot explorer · claude-haiku-5.5

I'm planning the structure of the fractal viewer: a full-screen canvas with pan/zoom state, rendering progressively in row chunks to avoid blocking the UI while computing.

I'm working out iteration counts and smooth coloring based on escape velocity, plus wheel-zoom logic that keeps the point under the cursor fixed while rescaling. I'm also setting initial view bounds so the full Mandelbrot set fits nicely on screen regardless of aspect ratio.

For interactivity, I'm handling resize by preserving center/scale, and panning by translating the center based on drag delta. To keep things responsive during drag or deep zoom, I'm planning time-sliced rendering with a generation counter so stale renders get cancelled when new ones start, since high iteration counts at full resolution can get computationally heavy.

I need to prevent default scroll behavior on wheel events and hide body overflow for a cleaner zoom experience, while verifying the cursor-anchor math keeps the point under the mouse fixed exactly. I'm also adding readouts for center, view height, and iteration count, plus scaling max iterations logarithmically with zoom depth, capping around a few thousand for performance. For the per-pixel loop, I'm converting screen coordinates to complex coordinates with y-axis flipped so imaginary values increase upward, and adding cardioid/period-2 bulb interior checks to skip unnecessary iterations and speed up rendering.

Now I'm structuring the chunked rendering: a generation counter cancels stale renders, and each time slice processes rows within a budget before painting just the dirty rectangle back to the canvas, looping via setTimeout until all rows finish. For coloring, I'm using a cosine-based palette that cycles hue smoothly based on the normalized iteration count.

For the Mandelbrot escape test, I'm using a large bailout radius (65536) combined with a smooth log-based normalization formula, plus early shortcuts to detect points inside the main cardioid or period-2 bulb without iterating. I'm sketching the inner pixel loop that tracks x, y, breaks on escape, and computes the smoothed iteration value, with panning handled via pointer drag events that also bump the render generation to cancel in-flight work.

I'm throttling renders during drag to one per animation frame via requestAnimationFrame rather than firing on every pointermove, accepting that partial/stale rows may briefly show while the budget-sliced render catches up. I'll also add a small HUD overlay showing render progress and timing, plus a reset button, before writing the file.

The screenshot only shows the top portion rendered, suggesting the render was captured too early at 15% progress rather than being complete. I'm double-checking the dirty-rect update logic used to paint the image incrementally, which looks correct, so the issue is likely just timing of when the screenshot was taken.

I'm also verifying the math: the cardioid shortcut check and the smooth-coloring normalization formula both hold up fine even with a large escape radius. The viewport settings centered near the main cardioid also seem right, so I'll grab another screenshot to confirm the render completes properly.

The render looks good with proper initial framing. Now I want to quickly test zoom, pan, and reset — I'll use the scroll action at a point to simulate zoom, then verify reset works, keeping the test brief.

I'm checking whether zooming at the cursor position correctly keeps the clicked point fixed, comparing the complex coordinates before and after the scroll to verify the center shift matches expectations.

I'm trying to figure out whether the cursor coordinates used for the zoom anchor actually match the pixel position I assumed, since the resulting center doesn't line up with my calculation—it seems the tool may be anchoring the scroll at a different point than I expected, and without more verification I can't pin down exactly where.

Since I can't run JS evaluation to confirm this directly, I'm planning a controlled test: reset the view, then scroll at a specific known pixel to see whether the resulting center matches my predicted formula, which should reveal the actual anchor mapping.

I notice something odd: the view center ends up the same for cursor positions at (700,200) and (300,400), which suggests the zoom anchor isn't actually tracking the cursor coordinates correctly. The wheel event might be dispatching at the wrong clientX/clientY, so I need to check how the anchor is computed from the old view before applying the new zoom.

My manual calculation gives a different predicted center than what was actually reported, which means the wheel events aren't landing at the coordinates I assumed. Rather than keep guessing at the anchor logic, I think it's better to just verify this empirically with a direct test instead of reasoning it out further.

Let me try one more test: reload, scroll at (900,600) with delta -400, then inspect after waiting to see if the center shifts consistently with the formula.

The scroll tool keeps producing the same zoom center of -1.0895 + 0.393i regardless of the x,y I give it, which makes me suspect the wheel event isn't actually using those coordinates—maybe it's always dispatched at a fixed point like the viewport center instead.

Given the time budget running low, I should be honest that I can't conclusively verify anchor precision through this harness since the scroll coordinates seem to always resolve to the same center point. I'll do one more quick check -- clicking reset and inspecting the result -- before wrapping up.

Reset behaves correctly, matching the initial state. But the wheel-anchoring math seems suspicious since the observed center stays identical regardless of cursor position—maybe the test harness isn't delivering real clientX/clientY values, defaulting them to zero.

The identical results across wheel positions make me suspect the scroll tool might not actually target specific coordinates, but the anchor math itself checks out analytically, so I'll trust the code and report what I observe honestly rather than overclaim precise cursor-anchoring verification. I'll do a final sanity check that the file is in place before wrapping up.