ShaderEffect messes up with opacity [answered]

asked 2015-10-27 02:04:31 +0300

kimmoli
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http://www.kimmoli.fi/

Just asking, am i doing something wrong...?

My fragmentShader to invert colors

// Invert colors

uniform sampler2D source;
uniform sampler2D mask;
varying highp vec2 qt_TexCoord0;
uniform lowp float qt_Opacity;

void main(void)
{
    highp vec4 color = texture2D(source, qt_TexCoord0);
    color.rgb = 1.0 - color.rgb;
    gl_FragColor = color * texture2D(mask, qt_TexCoord0).a;
}

where source contains the photo and the line-arts, and mask contains the white area

(i can write this in a few different ways, all resulting the same behaviour)

Results in this 20151027005718.jpg which changes to this 20151027005749.jpg if there is any activity on screen (e.g. rotating device is enough)

Another fragment shader to swap RGB channels (interesting part shown)

    gl_FragColor = texture2D(source, qt_TexCoord0).brga * texture2D(mask, qt_TexCoord0).a;

Results this: 20151027005635.jpg which is looking fine.

I know that the empty canvas is all black with alpha 0.0. I tried to replace clearRect() with filled rectangle of color Qt.rgba(1.0, 1.0, 1.0, 0.0) but it went even more haywire with that.

I tried to change the 1.0 - color.rgb to e.g. color.rgb + 0.1 and it fails in similar way. I see the transparent areas to get light white color.