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-rw-r--r--src/quick/items/qquickshadereffect.cpp23
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.