[MC-234030] Debug markers' colors no longer work

Hello,

The debug markers are really useful for developers to debug the game or even add new things to the game. Unfortunately since 1.17 the Blue and Red values of the color are no longer working.

What causes the issue?

The line:

fragColor = color * ColorModulator;

in the original assets assets/minecraft/shaders/core/position_color.fsh file:

#version 150
in vec4 vertexColor;
uniform vec4 ColorModulator;
out vec4 fragColor;
void main() {
 vec4 color = vertexColor;
 if (color.a == 0.0) {
 discard;
 }
 fragColor = color * ColorModulator;
}

Working fix (tested with a resourcepack), thanks to @DeltaEvo :

#version 150
in vec4 vertexColor;
uniform vec4 ColorModulator;
out vec4 fragColor;
void main() {
 vec4 color = vertexColor;
 if (color.a == 0.0) {
 discard;
 }
 if (ColorModulator == vec4(0.0f, 1.0f, 0.0f, 0.75f))
 fragColor = color;
 else
 fragColor = color * ColorModulator;
}

Please use the fixed version or similar in a future update!

Thank you,

Thomas

Comments 5

Andrew Herring 2021-11-17T19:37:46Z

Still not working on 1.18 pre-release 4... 😔

Andrew Herring 2021-11-23T15:38:48Z

Still not working on 1.18 pre-release 6

Andrew Herring 2021-11-26T03:47:18Z

Still not working on 1.18 Release Candidate 1

[Mod] Jingy 2024-07-25T23:11:55Z

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BugTracker_ 2026-03-14T17:52:41Z

This is still an issue as of 1.21.11.

Steps to Reproduce:

Extract the 1.21.11 client JAR.
Open assets/minecraft/shaders/core/position_color.fsh.
Observe that vertex color is unconditionally multiplied by ColorModulator on line 14.

Code Analysis:

#version 330

#moj_import <minecraft:dynamictransforms.glsl>

in vec4 vertexColor;

out vec4 fragColor;

void main() {
    vec4 color = vertexColor;
    if (color.a == 0.0) {
        discard;
    }
    fragColor = color * ColorModulator;
}

assets/minecraft/shaders/include/dynamictransforms.glsl:

#version 330

layout(std140) uniform DynamicTransforms {
    mat4 ModelViewMat;
    vec4 ColorModulator;
    vec3 ModelOffset;
    mat4 TextureMat;
};

Observed Results: The shader unconditionally multiplies vertex color by ColorModulator (fragColor = color * ColorModulator). When debug markers are rendered, ColorModulator is set to vec4(0.0, 1.0, 0.0, 0.75), which zeroes out the Red channel (×0.0) and distorts Blue/Alpha (×0.75). Only the Green channel passes through correctly. Though the shader has been upgraded from GLSL 150 to 330 and ColorModulator moved from a standalone uniform into a UBO (DynamicTransforms), the core issue remains unchanged.

Expected Results: Debug markers should render with their intended colors, including Red and Blue values, as they did prior to 1.17.