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feat: Add percentage support to CSS properties (#738)

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## Summary
- Closes #730

**What is the goal of this PR?**
- Adds percentage-based value support to CSS properties that accept
percentages (padding, margin, text-indent)
 
**What changes are included?**
- Adds `Percent` as another CSS unit
- Passes the viewport width to `fromCssStyle` so that we can resolve
percentage-based values
- Adds a fallback of using an emspace for text-indent if we have an
unresolvable value for whatever reason

## Additional Context

- This was missed in my CSS support feature, and the fallback when we
encounter a percentage value is to use px instead. This means 5% (which
would be ~30px on the screen) turns into 5px. When percentages are used
in `text-indent`, this fallback behavior makes the indent look like a
single space character. Whoops! 😬

My test EPUB has been updated
[here](https://github.com/jdk2pq/css-test-epub) with percentage based
CSS values at the end of the book.

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**YES**_, Claude Code
This commit is contained in:
Jake Kenneally
2026-02-09 08:31:52 +11:00
committed by GitHub
parent ffddc2472b
commit 9b04c2ec76
4 changed files with 38 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Epub/Epub/blocks/BlockStyle.h
+18 -12
View File
@@ -64,21 +64,27 @@ struct BlockStyle {
// Create a BlockStyle from CSS style properties, resolving CssLength values to pixels
// emSize is the current font line height, used for em/rem unit conversion
// paragraphAlignment is the user's paragraphAlignment setting preference
static BlockStyle fromCssStyle(const CssStyle& cssStyle, const float emSize, const CssTextAlign paragraphAlignment) {
static BlockStyle fromCssStyle(const CssStyle& cssStyle, const float emSize, const CssTextAlign paragraphAlignment,
const uint16_t viewportWidth = 0) {
BlockStyle blockStyle;
// Resolve all CssLength values to pixels using the current font's em size
blockStyle.marginTop = cssStyle.marginTop.toPixelsInt16(emSize);
blockStyle.marginBottom = cssStyle.marginBottom.toPixelsInt16(emSize);
blockStyle.marginLeft = cssStyle.marginLeft.toPixelsInt16(emSize);
blockStyle.marginRight = cssStyle.marginRight.toPixelsInt16(emSize);
const float vw = viewportWidth;
// Resolve all CssLength values to pixels using the current font's em size and viewport width
blockStyle.marginTop = cssStyle.marginTop.toPixelsInt16(emSize, vw);
blockStyle.marginBottom = cssStyle.marginBottom.toPixelsInt16(emSize, vw);
blockStyle.marginLeft = cssStyle.marginLeft.toPixelsInt16(emSize, vw);
blockStyle.marginRight = cssStyle.marginRight.toPixelsInt16(emSize, vw);
blockStyle.paddingTop = cssStyle.paddingTop.toPixelsInt16(emSize);
blockStyle.paddingBottom = cssStyle.paddingBottom.toPixelsInt16(emSize);
blockStyle.paddingLeft = cssStyle.paddingLeft.toPixelsInt16(emSize);
blockStyle.paddingRight = cssStyle.paddingRight.toPixelsInt16(emSize);
blockStyle.paddingTop = cssStyle.paddingTop.toPixelsInt16(emSize, vw);
blockStyle.paddingBottom = cssStyle.paddingBottom.toPixelsInt16(emSize, vw);
blockStyle.paddingLeft = cssStyle.paddingLeft.toPixelsInt16(emSize, vw);
blockStyle.paddingRight = cssStyle.paddingRight.toPixelsInt16(emSize, vw);
blockStyle.textIndent = cssStyle.textIndent.toPixelsInt16(emSize);
blockStyle.textIndentDefined = cssStyle.hasTextIndent();
// For textIndent: if it's a percentage we can't resolve (no viewport width),
// leave textIndentDefined=false so the EmSpace fallback in applyParagraphIndent() is used
if (cssStyle.hasTextIndent() && cssStyle.textIndent.isResolvable(vw)) {
blockStyle.textIndent = cssStyle.textIndent.toPixelsInt16(emSize, vw);
blockStyle.textIndentDefined = true;
}
blockStyle.textAlignDefined = cssStyle.hasTextAlign();
// User setting overrides CSS, unless "Book's Style" alignment setting is selected
if (paragraphAlignment == CssTextAlign::None) {