diff options
| -rw-r--r-- | src/quick/items/qquickshadereffect.cpp | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/src/quick/items/qquickshadereffect.cpp b/src/quick/items/qquickshadereffect.cpp index 05f82d558f..caabd541b6 100644 --- a/src/quick/items/qquickshadereffect.cpp +++ b/src/quick/items/qquickshadereffect.cpp @@ -110,7 +110,10 @@ QT_BEGIN_NAMESPACE \note It is only the vertex input location that matters in practice. The names are freely changeable, while the location must always be \c 0 for - vertex position, \c 1 for texture coordinates. + vertex position, \c 1 for texture coordinates. However, be aware that this + applies to vertex inputs only, and is not necessarily true for output + variables from the vertex shader that are then used as inputs in the + fragment shader (typically, the interpolated texture coordinates). The following uniforms are predefined: @@ -267,6 +270,18 @@ QT_BEGIN_NAMESPACE or the opacity, because at run time there is one single uniform buffer that is exposed to both the vertex and fragment shader. + \warning Unlike with vertex inputs, passing data between the vertex and + fragment shader may, depending on the underlying graphics API, require the + same names to be used, a matching location is not always sufficient. Most + prominently, when specifying a fragment shader while relying on the default, + built-in vertex shader, the texture coordinates are passed on as \c + qt_TexCoord0 at location \c 0, and therefore it is strongly advised that the + fragment shader declares the input with the same name + (qt_TexCoord0). Failing to do so may lead to issues on some platforms, for + example when running with a non-core profile OpenGL context where the + underlying GLSL shader source code has no location qualifiers and matching + is based on the variable names during to shader linking process. + \section1 ShaderEffect and Item Layers The ShaderEffect type can be combined with \l {Item Layers} {layered items}. @@ -436,7 +451,11 @@ QT_BEGIN_NAMESPACE \li The vertex shader outputs and fragment shader inputs are up to the shader code to define. The fragment shader must have a \c vec4 output at - location 0 (typically called \c fragColor). + location 0 (typically called \c fragColor). For maximum portability, vertex + outputs and fragment inputs should use both the same location number and the + same name. When specifying only a fragment shader, the texture coordinates + are passed in from the built-in vertex shader as \c{vec2 qt_TexCoord0} at + location \c 0, as shown in the example snippets above. \li Uniform variables outside a uniform block are not legal. Rather, uniform data must be declared in a uniform block with binding point \c 0. |