@@ -31,6 +31,7 @@ int main()

     // Use.

     player

+        .use()

         .validate();

 }

 ```

@@ -116,7 +117,9 @@ OpenGL state to make sure that a subsequent draw call would succeed. An error

 is thrown if a problem is detected.

 Additional issues that are not typically detected by [`glValidateProgram`][]

-are checked for.

+are checked for:

+

+-   Shader program not [current](#use).

 If the macro [`NDEBUG`][] is defined, the check is optimised out. Therefore, it

 is recommended to always call `validate()` before issuing draw calls.

@@ -125,6 +128,16 @@ is recommended to always call `validate()` before issuing draw calls.

 [`glValidateProgram`]: https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glValidateProgram.xhtml

 [`NDEBUG`]: https://en.cppreference.com/w/c/error/assert

+### Use

+

+The shader needs to be [use][]d by calling `use()` before performing certain

+other actions on it.

+

+If the macro [`NDEBUG`][] is not defined, an error is thrown if this is not the

+case.

+

+[use]: https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glUseProgram.xhtml

+

 ## Dependencies

 Public (interface):

new file mode 100644

@@ -0,0 +1,7 @@

+#version 110

+

+

+void main()

+{

+    gl_Position = gl_Vertex;

+}

Binary files a/assets/tests/frame.data and b/assets/tests/frame.data differ

@@ -26,10 +26,14 @@ public:

     GLuint program() const;

     Shader & validate();

+    Shader & use();

 protected:

     void validate_() const;

+    void current_(

+        std::string const & error

+    ) const;

     GLuint             program_;

     std::string        program_name_;

@@ -66,5 +70,11 @@ inline Shader & Shader::validate()

     return *this;

 }

+inline Shader & Shader::use()

+{

+    glUseProgram(program_);

+    return *this;

+}

+

 #endif // GLSHADER_SHADER_HPP_

@@ -229,4 +229,18 @@ void Shader::validate_() const

         glValidateProgram, program_,

         GL_VALIDATE_STATUS, glGetProgramiv, glGetProgramInfoLog

     );

+

+    // Assert current.

+    current_(validate_error);

+}

+

+

+void Shader::current_(std::string const & error) const

+{

+    // Error if not current.

+    if (get_integer_<GLuint>(GL_CURRENT_PROGRAM) != program_)

+        throw std::runtime_error{STR(

+            error << "; " <<

+            "shader program not current."

+        )};

 }

@@ -46,12 +46,20 @@ GLTEST(2, 0, 640, 480, glshader)

         "active samplers with a different type refer to the same texture image unit"

     )

+    // Use.

+    GLTEST_EXPECT_EXCEPTION(false,

+        Shader({"tests/use.vert"}).validate(),

+        "Failed to validate shader program 'tests/use.vert'; "

+        "shader program not current."

+    )

+

     auto all = Shader({

         "tests/all.vert",

         "tests/all.frag",

     });

     all

+        .use()

         .validate();

     constexpr auto size = 0.5F;