Skip to content

(Un)premultiply colors in begin/end modify image + another fix #10

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
flabbet merged 2 commits into from
Aug 18, 2026
Merged

(Un)premultiply colors in begin/end modify image + another fix #10

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
d463b62
Fix #1678 - introduce unpremultiplication and premultiplication to be…
Equbuxu Aug 12, 2026
c38a8f0
Fix #1680: make sure the 'color' in layout(color) isn't replaced when…
Equbuxu Aug 12, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
13 changes: 13 additions & 0 deletions src/Drawie.Backend.Core/Shaders/Generation/BuiltInFunctions.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,8 @@ public partial class BuiltInFunctions

private const string Epsilon = "1e-10";

public Expression GetUnpremultiply(Expression rgbaHalf4) => Call(Unpremultiply, rgbaHalf4);

public Expression GetRgbToHsv(Expression rgba) => Call(RgbToHsv, rgba);

public Expression GetRgbToHsl(Expression rgba) => Call(RgbToHsl, rgba);
Expand Down Expand Up @@ -65,6 +67,17 @@ private void Require(IBuiltInFunction function)
usedFunctions.Add(function);
}

private static readonly BuiltInFunction<Half4> Unpremultiply = new(
"half4 color",
nameof(Unpremultiply),
"""
if (color.a <= 0.0) {
return half4(0, 0, 0, 0);
}
return half4(color.rgb / color.a, color.a);
"""
);

// Taken from here https://www.shadertoy.com/view/4dKcWK
private static readonly BuiltInFunction<Half3> HueToRgb = new(
"float hue",
Expand Down
21 changes: 15 additions & 6 deletions src/Drawie.Backend.Core/Shaders/Generation/ShaderBuilder.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -83,20 +83,29 @@ public SurfaceSampler AddOrGetSurface(DrawingSurface surface, ColorSampleMode sa

public Half4 Sample(SurfaceSampler texName, Expression pos, bool normalizedCoordinates)
{
string resultName = $"color_{GetUniqueNameNumber()}";
Half4 result = new Half4(resultName);
_variables.Add(result);
string rawResultName = $"color_{GetUniqueNameNumber()}";
Half4 rawResult = new Half4(rawResultName);
_variables.Add(rawResult);

string unpremulResultName = $"color_{GetUniqueNameNumber()}";
Half4 unpremulResult = new Half4(unpremulResultName);
_variables.Add(unpremulResult);

if (normalizedCoordinates)
{
_bodyBuilder.AppendLine(
$"half4 {resultName} = {texName.VariableName}.eval({pos.ExpressionValue} * iResolution);");
$"half4 {rawResultName} = {texName.VariableName}.eval({pos.ExpressionValue} * iResolution);");
_bodyBuilder.AppendLine(
$"half4 {unpremulResultName} = {Functions.GetUnpremultiply(rawResult).ExpressionValue};");
}
else
{
_bodyBuilder.AppendLine($"half4 {resultName} = {texName.VariableName}.eval({pos.ExpressionValue});");
_bodyBuilder.AppendLine($"half4 {rawResultName} = {texName.VariableName}.eval({pos.ExpressionValue});");
_bodyBuilder.AppendLine(
$"half4 {unpremulResultName} = {Functions.GetUnpremultiply(rawResult).ExpressionValue};");
}

return result;
return unpremulResult;
}

public void ReturnVar(Half4 colorValue, bool premultiply)
Expand Down
10 changes: 9 additions & 1 deletion src/Drawie.Backend.Skia/Implementations/SkiaShaderImplementation.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -553,6 +553,14 @@ internal static List<UniformDeclaration> DeclarationsFromEffect(string code, SKR
return null;
}

private static string RemoveLastOccurance(string text, string toRemove)
{
int index = text.LastIndexOf(toRemove, StringComparison.Ordinal);
return index < 0 ?
text :
text.Substring(0, index) + text.Substring(index + toRemove.Length);
}

private static bool TryDetectType(string lastString, string name, out UniformValueType? detectedType)
{
if (!lastString.Contains("uniform ", StringComparison.InvariantCultureIgnoreCase))
Expand All @@ -561,7 +569,7 @@ private static bool TryDetectType(string lastString, string name, out UniformVal
return false;
}

string nameLessBlock = lastString.Replace(name, string.Empty);
string nameLessBlock = RemoveLastOccurance(lastString, name);

if (nameLessBlock.Contains("color", StringComparison.InvariantCultureIgnoreCase))
{
Expand Down