Is it forbidden to change the value of an in-variable inside a fragment shader? The following code crashes exactly when I try to set a new value to "doseValue" :
const GLchar *point_fragment_shader =
"#version 420\n"
""
"/* Per Fragment Input Attributes */"
"in float doseValue;"
"in float alphaValue;"
"in vec2 displayUncertaintyByChangedColor;"
""
"/* Uniform Attributes */"
"uniform float minDisplayDoseValue;"
"uniform int pointVisualizationMode;"
""
"/* Per Fragment Output Values */"
"out vec4 out_color;"
""
"void main()"
"{"
" "
" /* Discard all Points whose dose value is below the minimum */"
" if(doseValue < minDisplayDoseValue)"
" {"
" discard;"
" }"
" else"
" {"
" if(displayUncertaintyByChangedColor.x == 1.0)"
" {"
" doseValue = 500.0;"
" }"
" ..."
Inside the vec2, the first component is 0.0 or 1.0, the second is some floating point number. If I set up a new variable and initialize it with some arbitrary value inside the second if-statement, there's no error.