issue: when an image is displayed on this camera and contains a glow effect, it becomes black

Edit 1:

I tried to add the suggested glBlendFunc and it didn't help although it affected the glow effect a little bit. I needed to add GLES20.glEnable(GLES20.GL_BLEND) because it's disabled by default.

---------------------------

I'm using this repository

https://github.com/MasayukiSuda/GPUVideo-android

It contains filters that can be displayed on the camera. One of the filters is named "WATERMARK". When I change this image to be an image with a glow effect, the glow becomes black.

The image is located at: GPUVideo-android-master\sample\src\main\res\drawable-nodpi\sample_bitmap.png. In order to trigger the problem, it should be changed to an image with glow effect. For example I generated this image: https://drive.google.com/file/d/1u8PtIftovPbXRLnI3OR9_1Kv37L5s96_/view?usp=sharing

You can see the issue with the white glow effect that becomes black:

Just run the app, click on "Camera Record", then choose "Portrait" and from the left list choose "WATERMARK" (the 5th from the end). Don't forget to change the image I mentioned.

The relevant class is named: GlWatermarkFilter. It extends GlOverlayFilter which contains the next shader:

 private final static String FRAGMENT_SHADER =
        "precision mediump float;\n" +
                "varying vec2 vTextureCoord;\n" +
                "uniform lowp sampler2D sTexture;\n" +
                "uniform lowp sampler2D oTexture;\n" +
                "void main() {\n" +
                "   lowp vec4 textureColor = texture2D(sTexture, vTextureCoord);\n" +
                "   lowp vec4 textureColor2 = texture2D(oTexture, vTextureCoord);\n" +
                "   \n" +
                "   gl_FragColor = mix(textureColor, textureColor2, textureColor2.a);\n" +
                "}\n";

and this class also contains this setup:

GLES20.glGenTextures(1, textures, 0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);

GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);

This class extends GlFilter which contains:

protected static final String DEFAULT_VERTEX_SHADER =
        "attribute highp vec4 aPosition;\n" +
                "attribute highp vec4 aTextureCoord;\n" +
                "varying highp vec2 vTextureCoord;\n" +
                "void main() {\n" +
                "gl_Position = aPosition;\n" +
                "vTextureCoord = aTextureCoord.xy;\n" +
                "}\n";

protected static final String DEFAULT_FRAGMENT_SHADER =
        "precision mediump float;\n" +
                "varying highp vec2 vTextureCoord;\n" +
                "uniform lowp sampler2D sTexture;\n" +
                "void main() {\n" +
                "gl_FragColor = texture2D(sTexture, vTextureCoord);\n" +
                "}\n";

Please help me to figure out how to fix it. I know it's something about semi-alpha issue and this camera that doesn't know to display it. My goal is to record a video with glowing butterflies.

from issue: when an image is displayed on this camera and contains a glow effect, it becomes black