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Rigorous unordered list detection and feature-complete indentation support #42

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f175ad1
This should be sensible
JoshuaMKW Jan 12, 2026
825a955
Fix bugs
JoshuaMKW Jan 12, 2026
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186 changes: 143 additions & 43 deletions imgui_markdown.h
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Original file line number Diff line number Diff line change
Expand Up @@ -235,6 +235,8 @@ enum ImGuiMarkdownFormatFlags_
ImGuiMarkdownFormatFlags_DiscardExtraNewLines = 1 << 0, // (Accurate parsing) Provided markdown will discard all redundant newlines
ImGuiMarkdownFormatFlags_NoNewLineBeforeHeading = 1 << 1, // (Accurate parsing) Provided markdown will not format a newline after the first line if it is a heading
ImGuiMarkdownFormatFlags_SeparatorDoesNotAdvance = 1 << 2, // (Accurate parsing) Provided markdown will not advance to the next line after formatting a separator
ImGuiMarkdownFormatFlags_ExoticIndents = 1 << 3, // (Accurate parsing) Provided markdown will process indents based on number of leading spaces rather than fixed 2-space indents
ImGuiMarkdownFormatFlags_IncludeAllListPrefixes = 1 << 4, // (Accurate parsing) Provided markdown will include all list prefixes such as '-', '+', '*' for unordered lists and '1.', '2.' etc. for ordered lists, rather than just '*'
ImGuiMarkdownFormatFlags_GithubStyle = ImGuiMarkdownFormatFlags_DiscardExtraNewLines | ImGuiMarkdownFormatFlags_NoNewLineBeforeHeading | ImGuiMarkdownFormatFlags_SeparatorDoesNotAdvance,
ImGuiMarkdownFormatFlags_CommonMarkAll = ImGuiMarkdownFormatFlags_DiscardExtraNewLines | ImGuiMarkdownFormatFlags_NoNewLineBeforeHeading | ImGuiMarkdownFormatFlags_SeparatorDoesNotAdvance,
};
Expand Down Expand Up @@ -332,6 +334,7 @@ namespace ImGui
struct MarkdownConfig
{
static const int NUMHEADINGS = 3;
static const int INDENTSTACKSIZE = 8; // Internal use only

MarkdownLinkCallback* linkCallback = NULL;
MarkdownTooltipCallback* tooltipCallback = NULL;
Expand All @@ -357,6 +360,7 @@ namespace ImGui
struct Line;
inline void UnderLine( ImColor col_ );
inline void RenderLine( const char* markdown_, Line& line_, TextRegion& textRegion_, const MarkdownConfig& mdConfig_ );
inline Line* DetectTargetLineAsIndent( const Line& self, Line indentLines_[MarkdownConfig::INDENTSTACKSIZE], int indentLinesCount_, bool& isDeeplyNested_ );

struct TextRegion
{
Expand Down Expand Up @@ -400,11 +404,12 @@ namespace ImGui
struct Line {
bool isHeading = false;
bool isEmphasis = false;
bool isUnorderedListStart = false;
char unorderedListChar = '\0';
bool isLeadingSpace = true; // spaces at start of line
int leadSpaceCount = 0;
int headingCount = 0;
int emphasisCount = 0;
int indentCount = 0;
int lineStart = 0;
int lineEnd = 0;
int lastRenderPosition = 0; // lines may get rendered in multiple pieces
Expand Down Expand Up @@ -456,12 +461,7 @@ namespace ImGui
inline void RenderLine( const char* markdown_, Line& line_, TextRegion& textRegion_, const MarkdownConfig& mdConfig_ )
{
// indent
int indentStart = 0;
if( line_.isUnorderedListStart ) // ImGui unordered list render always adds one indent
{
indentStart = 1;
}
for( int j = indentStart; j < line_.leadSpaceCount / 2; ++j ) // add indents
for( int j = 0; j < line_.indentCount; ++j ) // add indents
{
ImGui::Indent();
}
Expand All @@ -471,7 +471,7 @@ namespace ImGui
formatInfo.config = &mdConfig_;
int textStart = line_.lastRenderPosition + 1;
int textSize = line_.lineEnd - textStart;
if( line_.isUnorderedListStart ) // render unordered list
if( line_.unorderedListChar != '\0' ) // render unordered list
{
formatInfo.type = MarkdownFormatType::UNORDERED_LIST;
mdConfig_.formatCallback( formatInfo, true );
Expand Down Expand Up @@ -506,12 +506,48 @@ namespace ImGui
mdConfig_.formatCallback( formatInfo, false );

// unindent
for( int j = indentStart; j < line_.leadSpaceCount / 2; ++j )
for( int j = 0; j < line_.indentCount; ++j )
{
ImGui::Unindent();
}
}

inline Line* DetectTargetLineAsIndent( const Line& self, Line indentLines_[MarkdownConfig::INDENTSTACKSIZE], int indentLinesCount_, bool& isDeeplyNested )
{
isDeeplyNested = false;
if (indentLinesCount_ >= MarkdownConfig::INDENTSTACKSIZE)
{
return nullptr; // too deep nesting
}
else
{
if (indentLinesCount_ > 0) // Sub-lists have special handling from root lists
{
// We traverse the list bottom-up to see if we are in a sub-list
for (int j = indentLinesCount_ - 1; j >= 0; --j)
{
Line* listLine = indentLines_ + j;
int indentDiff = self.leadSpaceCount - listLine->leadSpaceCount;
if (indentDiff > 5) // Too many spaces, not a sub-list
{
isDeeplyNested = true;
return nullptr;
}

if (indentDiff >= 2) // Sub-lists have at least 2 spaces more indent
{
return listLine;
}
}
return nullptr;
}
else
{
return nullptr; // Root list
}
}
}

// render markdown
inline void Markdown( const char* markdown_, size_t markdownLength_, const MarkdownConfig& mdConfig_ )
{
Expand All @@ -533,6 +569,10 @@ namespace ImGui
int concurrentEmptyNewlines = 0;
bool appliedExtraNewline = false;

Line lineIndentStack[MarkdownConfig::INDENTSTACKSIZE];
int lineIndentStackCount = 0;
int nextIndentStackCount = -1;

char c = 0;
for( int i=0; i < (int)markdownLength_; ++i )
{
Expand All @@ -542,6 +582,18 @@ namespace ImGui
// If we're at the beginning of the line, count any spaces
if( line.isLeadingSpace )
{
if ( (mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_ExoticIndents) )
{
if ( c == '\n' )
{
lineIndentStackCount = 0; // reset indents on multiple newlines
}
else if ( ( c == '\r' ) && ( (int)markdownLength_ > i + 1 ) && ( markdown_[i + 1] == '\n' ) )
{
lineIndentStackCount = 0; // reset indents on multiple newlines
}
}

if ( (mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_DiscardExtraNewLines) ) // Discard LF and CRLF newlines by markdown spec
{
if ( c == '\n' )
Expand All @@ -568,46 +620,83 @@ namespace ImGui
{
line.isLeadingSpace = false;
line.lastRenderPosition = i - 1;
if(( c == '*' ) && ( line.leadSpaceCount >= 2 ))
bool isDeeplyNested = false;
Line* targetIndentLine = nullptr;
if ( mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_ExoticIndents )
{
if( ( (int)markdownLength_ > i + 1 ) && ( markdown_[ i + 1 ] == ' ' ) ) // space after '*'
{
line.isUnorderedListStart = true;
++i;
++line.lastRenderPosition;
}
// carry on processing as could be emphasis
targetIndentLine = DetectTargetLineAsIndent(line, lineIndentStack, lineIndentStackCount, isDeeplyNested);
// This is assuming plain-text, which is tabbed to the deepest indentation on the stack
line.indentCount = lineIndentStackCount > 0 ? lineIndentStack[lineIndentStackCount - 1].indentCount + 1 : 0;
}
else if( c == '#' )
else
{
line.headingCount++;
bool bContinueChecking = true;
int j = i;
while( ++j < (int)markdownLength_ && bContinueChecking )
line.indentCount = line.leadSpaceCount / 2;
}
// Deeply nested text always acts as plain-text, regardless of characters found
if ( !isDeeplyNested ) // this is always false without ImGuiMarkdownFormatFlags_ExoticIndents
{
bool marksUnorderedListing = ( mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_IncludeAllListPrefixes ) ? ( c == '*' || c == '-' || c == '+' ) : ( c == '*' );
marksUnorderedListing &= ( (int)markdownLength_ > i + 1 ) && ( markdown_[ i + 1 ] == ' ' );
if ( mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_ExoticIndents )
{
if ( !targetIndentLine )
{
marksUnorderedListing &= line.leadSpaceCount < 4; // root lists require less than 4 leading spaces
}
}
else
{
marksUnorderedListing &= line.leadSpaceCount >= 2; // default imgui_markdown behavior
}
if ( marksUnorderedListing )
{
c = markdown_[j];
switch( c )
line.unorderedListChar = c;
++i;
++line.lastRenderPosition;
if ( mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_ExoticIndents )
{
case '#':
line.headingCount++;
break;
case ' ':
line.lastRenderPosition = j - 1;
i = j;
line.isHeading = true;
bContinueChecking = false;
break;
default:
line.isHeading = false;
bContinueChecking = false;
break;
// This is for unordered lists, rather than plain-text
line.indentCount = targetIndentLine ? targetIndentLine->indentCount + 1 : 0;
nextIndentStackCount = line.indentCount + 1;
}
}
if( line.isHeading )
else if( c == '#' )
{
// reset emphasis status, we do not support emphasis around headers for now
em = Emphasis();
continue;
line.headingCount++;
bool bContinueChecking = true;
int j = i;
while( ++j < (int)markdownLength_ && bContinueChecking )
{
c = markdown_[j];
switch( c )
{
case '#':
line.headingCount++;
break;
case ' ':
line.lastRenderPosition = j - 1;
i = j;
line.isHeading = true;
if ( ( mdConfig_.formatFlags & ImGuiMarkdownFormatFlags_ExoticIndents ) )
{
// Headings act as lists do, except child lines are not allowed, so they retreat
line.indentCount = targetIndentLine ? targetIndentLine->indentCount + 1 : 0;
nextIndentStackCount = line.indentCount;
}
bContinueChecking = false;
break;
default:
line.isHeading = false;
bContinueChecking = false;
break;
}
}
if( line.isHeading )
{
// reset emphasis status, we do not support emphasis around headers for now
em = Emphasis();
continue;
}
}
}
}
Expand Down Expand Up @@ -670,7 +759,7 @@ namespace ImGui
RenderLine( markdown_, line, textRegion, mdConfig_ );
line.leadSpaceCount = 0;
link.url.stop = i;
line.isUnorderedListStart = false; // the following text shouldn't have bullets
line.unorderedListChar = '\0'; // the following text shouldn't have bullets
ImGui::SameLine( 0.0f, 0.0f );
if( link.isImage ) // it's an image, render it.
{
Expand Down Expand Up @@ -788,7 +877,7 @@ namespace ImGui
line.lineEnd = lineEnd;
RenderLine( markdown_, line, textRegion, mdConfig_ );
ImGui::SameLine( 0.0f, 0.0f );
line.isUnorderedListStart = false;
line.unorderedListChar = '\0';
line.leadSpaceCount = 0;
}
line.isEmphasis = true;
Expand Down Expand Up @@ -837,13 +926,24 @@ namespace ImGui
RenderLine( markdown_, line, textRegion, mdConfig_ );
}

if( 0 < nextIndentStackCount && nextIndentStackCount < MarkdownConfig::INDENTSTACKSIZE )
{
lineIndentStack[nextIndentStackCount - 1] = line;
lineIndentStackCount = nextIndentStackCount;
}
else if ( nextIndentStackCount == 0 )
{
lineIndentStackCount = 0;
}

// reset the line and emphasis state
prevLine = line;
line = Line();
em = Emphasis();

line.lineStart = i + 1;
line.lastRenderPosition = i;
nextIndentStackCount = -1;

textRegion.ResetIndent();

Expand Down