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Fix CairoMakie heatmap cell sizes #3625

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Fix CairoMakie heatmap cell sizes #3625

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b0798f8
fix CairoMakie heatmap cell sizes
Feb 12, 2024
def0bbb
calculate margin per pixel individually
Feb 12, 2024
d855982
compute dx only when needed
Feb 13, 2024
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21 changes: 10 additions & 11 deletions CairoMakie/src/primitives.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -777,21 +777,20 @@ function _draw_rect_heatmap(ctx, xys, ni, nj, colors, margin_factor=0.05f0)
p2 = xys[i+1, j]
p3 = xys[i+1, j+1]
p4 = xys[i, j+1]

# dx and dy are the margin widths that are added to the
# heatmap cell sizes further down
# adding 5% seems like a good compromise between avoiding artifacts
# and not changing pixel sizes too much
# how much is added can be controlled via margin_factor

dx = abs(p2[1] - p1[1]) * 0.5f0 * margin_factor
dy = abs(p4[2] - p1[2]) * 0.5f0 * margin_factor


# Rectangles and polygons that are directly adjacent usually show
# white lines between them due to anti aliasing. To avoid this we
# increase their size slightly.

if alpha(colors[i, j]) == 1 && margin_factor > 0
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What happens if using a transparent colormap here?

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The problem mostly goes away, but when you set alpha=0.99 for example, there are still some cases where artifacts occur. For example thin lines that shouldn't be there.

# dx and dy are the margin widths that are added to the
# heatmap cell sizes further down
# adding 5% seems like a good compromise between avoiding artifacts
# and not changing pixel sizes too much
# how much is added can be controlled via margin_factor
dx = abs(p2[1] - p1[1]) * 0.5f0 * margin_factor
dy = abs(p4[2] - p1[2]) * 0.5f0 * margin_factor

# sign.(p - center) gives the direction in which we need to
# extend the polygon. (Which may change due to rotations in the
# model matrix.) (i!=1) etc is used to avoid increasing the
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