NoInit constructor for AbstractShaderProgram.

Also made it possible to call AbstractShaderProgram destructor without
an GL context being active.

src/Magnum/AbstractShaderProgram.cpp

@@ -277,16 +277,20 @@ AbstractShaderProgram::AbstractShaderProgram(): _id(glCreateProgram()) {
     CORRADE_INTERNAL_ASSERT(_id != Implementation::State::DisengagedBinding);
 }
 
+AbstractShaderProgram::AbstractShaderProgram(NoCreateT) noexcept: _id{0} {}
+
 AbstractShaderProgram::AbstractShaderProgram(AbstractShaderProgram&& other) noexcept: _id(other._id) {
     other._id = 0;
 }
 
 AbstractShaderProgram::~AbstractShaderProgram() {
+    if(!_id) return;
+
     /* Remove current usage from the state */
     GLuint& current = Context::current().state().shaderProgram->current;
     if(current == _id) current = 0;
 
-    if(_id) glDeleteProgram(_id);
+    glDeleteProgram(_id);
 }
 
 AbstractShaderProgram& AbstractShaderProgram::operator=(AbstractShaderProgram&& other) noexcept {

src/Magnum/AbstractShaderProgram.h

@@ -35,6 +35,7 @@
 
 #include "Magnum/AbstractObject.h"
 #include "Magnum/Attribute.h"
+#include "Magnum/Tags.h"
 
 #if defined(CORRADE_TARGET_WINDOWS) && !defined(MAGNUM_TARGET_GLES2)
 #include <vector>
@@ -695,6 +696,19 @@ class MAGNUM_EXPORT AbstractShaderProgram: public AbstractObject {
          */
         explicit AbstractShaderProgram();
 
+        /**
+         * @brief Construct without creating the underlying OpenGL object
+         *
+         * The constructed instance is equivalent to moved-from state. Useful
+         * in cases where you will overwrite the instance later anyway. Move
+         * another object over it to make it useful.
+         *
+         * This function can be safely used for constructing (and later
+         * destructing) objects even without any OpenGL context being active.
+         * @see @ref AbstractShaderProgram()
+         */
+        explicit AbstractShaderProgram(NoCreateT) noexcept;
+
         /** @brief Copying is not allowed */
         AbstractShaderProgram(const AbstractShaderProgram&) = delete;
 

src/Magnum/Test/AbstractShaderProgramTest.cpp

@@ -0,0 +1,56 @@
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016
+              Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#include <Corrade/TestSuite/Tester.h>
+
+#include "Magnum/AbstractShaderProgram.h"
+
+namespace Magnum { namespace Test {
+
+struct AbstractShaderProgramTest: TestSuite::Tester {
+    explicit AbstractShaderProgramTest();
+
+    void constructNoCreate();
+};
+
+AbstractShaderProgramTest::AbstractShaderProgramTest() {
+    addTests({&AbstractShaderProgramTest::constructNoCreate});
+}
+
+void AbstractShaderProgramTest::constructNoCreate() {
+    {
+        struct: AbstractShaderProgram {
+            using AbstractShaderProgram::AbstractShaderProgram;
+        } shader{NoCreate};
+
+        CORRADE_COMPARE(shader.id(), 0);
+    }
+
+    CORRADE_VERIFY(true);
+}
+
+}}
+
+CORRADE_TEST_MAIN(Magnum::Test::AbstractShaderProgramTest)

src/Magnum/Test/CMakeLists.txt

@@ -25,6 +25,7 @@
 
 corrade_add_test(ArrayTest ArrayTest.cpp LIBRARIES Magnum)
 corrade_add_test(AttributeTest AttributeTest.cpp LIBRARIES Magnum)
+corrade_add_test(AbstractShaderProgramTest AbstractShaderProgramTest.cpp LIBRARIES Magnum)
 corrade_add_test(BufferTest BufferTest.cpp LIBRARIES Magnum)
 corrade_add_test(FormatTest FormatTest.cpp LIBRARIES Magnum)
 corrade_add_test(ContextTest ContextTest.cpp LIBRARIES Magnum)