OpenGL: Check at runtime whether non-power-of-two textures are supported

modules/juce_opengl/opengl/juce_OpenGLContext.cpp

@@ -69,6 +69,24 @@ private:
  extern JUCE_API double getScaleFactorForWindow (HWND);
 #endif
 
+static bool contextHasTextureNpotFeature()
+{
+    if (getOpenGLVersion() >= Version (2))
+        return true;
+
+    // If the version is < 2, we can't use the newer extension-checking API
+    // so we have to use glGetString
+    const auto* extensionsBegin = glGetString (GL_EXTENSIONS);
+
+    if (extensionsBegin == nullptr)
+        return false;
+
+    const auto* extensionsEnd = findNullTerminator (extensionsBegin);
+    const std::string extensionsString (extensionsBegin, extensionsEnd);
+    const auto stringTokens = StringArray::fromTokens (extensionsString.c_str(), false);
+    return stringTokens.contains ("GL_ARB_texture_non_power_of_two");
+}
+
 //==============================================================================
 class OpenGLContext::CachedImage  : public CachedComponentImage,
                                     private ThreadPoolJob
@@ -530,6 +548,8 @@ public:
         shadersAvailable = OpenGLShaderProgram::getLanguageVersion() > 0;
         clearGLError();
 
+        textureNpotSupported = contextHasTextureNpotFeature();
+
         if (context.renderer != nullptr)
             context.renderer->newOpenGLContextCreated();
 
@@ -665,6 +685,7 @@ public:
    #else
     bool shadersAvailable = false;
    #endif
+    bool textureNpotSupported = false;
     std::atomic<bool> hasInitialised { false }, needsUpdate { true }, destroying { false };
     uint32 lastMMLockReleaseTime = 0;
 
@@ -1068,6 +1089,12 @@ bool OpenGLContext::areShadersAvailable() const
     return c != nullptr && c->shadersAvailable;
 }
 
+bool OpenGLContext::isTextureNpotSupported() const
+{
+    auto* c = getCachedImage();
+    return c != nullptr && c->textureNpotSupported;
+}
+
 ReferenceCountedObject* OpenGLContext::getAssociatedObject (const char* name) const
 {
     jassert (name != nullptr);

modules/juce_opengl/opengl/juce_OpenGLContext.h

@@ -130,6 +130,9 @@ public:
     /** Returns true if shaders can be used in this context. */
     bool areShadersAvailable() const;
 
+    /** Returns true if non-power-of-two textures are supported in this context. */
+    bool isTextureNpotSupported() const;
+
     /** OpenGL versions, used by setOpenGLVersionRequired(). */
     enum OpenGLVersion
     {

modules/juce_opengl/opengl/juce_OpenGLTexture.cpp

@@ -26,15 +26,6 @@
 namespace juce
 {
 
-static int getAllowedTextureSize (int x)
-{
-   #if JUCE_OPENGL_ALLOW_NON_POWER_OF_TWO_TEXTURES
-    return x;
-   #else
-    return nextPowerOfTwo (x);
-   #endif
-}
-
 OpenGLTexture::OpenGLTexture()
     : textureID (0), width (0), height (0), ownerContext (nullptr)
 {
@@ -80,6 +71,13 @@ void OpenGLTexture::create (const int w, const int h, const void* pixels, GLenum
     glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
     JUCE_CHECK_OPENGL_ERROR
 
+    const auto textureNpotSupported = ownerContext->isTextureNpotSupported();
+
+    const auto getAllowedTextureSize = [&] (int n)
+    {
+        return textureNpotSupported ? n : nextPowerOfTwo (n);
+    };
+
     width  = getAllowedTextureSize (w);
     height = getAllowedTextureSize (h);