opengl: require support for fbos

It's effectively required already, as they're used everywhere

src/opengl/glframebuffer.cpp

@@ -22,12 +22,10 @@ namespace KWin
 void GLFramebuffer::initStatic()
 {
     if (GLPlatform::instance()->isGLES()) {
-        s_supported = true;
         s_supportsPackedDepthStencil = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_OES_packed_depth_stencil"));
         s_supportsDepth24 = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_OES_depth24"));
         s_blitSupported = hasGLVersion(3, 0);
     } else {
-        s_supported = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_ARB_framebuffer_object")) || hasGLExtension(QByteArrayLiteral("GL_EXT_framebuffer_object"));
         s_supportsPackedDepthStencil = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_ARB_framebuffer_object")) || hasGLExtension(QByteArrayLiteral("GL_EXT_packed_depth_stencil"));
         s_blitSupported = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_ARB_framebuffer_object")) || hasGLExtension(QByteArrayLiteral("GL_EXT_framebuffer_blit"));
     }
@@ -36,7 +34,6 @@ void GLFramebuffer::initStatic()
 void GLFramebuffer::cleanup()
 {
     Q_ASSERT(s_fbos.isEmpty());
-    s_supported = false;
     s_blitSupported = false;
 }
 
@@ -109,11 +106,6 @@ GLFramebuffer::GLFramebuffer(GLTexture *colorAttachment, Attachment attachment)
     : m_size(colorAttachment->size())
     , m_colorAttachment(colorAttachment)
 {
-    if (!s_supported) {
-        qCCritical(KWIN_OPENGL) << "Framebuffer objects aren't supported!";
-        return;
-    }
-
     GLuint prevFbo = 0;
     if (const GLFramebuffer *current = currentFramebuffer()) {
         prevFbo = current->handle();

src/opengl/glframebuffer.h

@@ -82,10 +82,6 @@ public:
     }
 
     static void initStatic();
-    static bool supported()
-    {
-        return s_supported;
-    }
 
     /**
      * Returns the last bound framebuffer, or @c null if no framebuffer is current.
@@ -138,7 +134,6 @@ private:
 
     friend void KWin::cleanupGL();
     static void cleanup();
-    inline static bool s_supported = false;
     inline static bool s_supportsPackedDepthStencil = false;
     inline static bool s_supportsDepth24 = false;
     inline static bool s_blitSupported = false;

src/opengl/gltexture.cpp

@@ -29,7 +29,6 @@ namespace KWin
 // GLTexture
 //****************************************
 
-bool GLTexturePrivate::s_supportsFramebufferObjects = false;
 bool GLTexturePrivate::s_supportsARGB32 = false;
 bool GLTexturePrivate::s_supportsUnpack = false;
 bool GLTexturePrivate::s_supportsTextureStorage = false;
@@ -144,7 +143,6 @@ GLTexturePrivate::~GLTexturePrivate()
 void GLTexturePrivate::initStatic()
 {
     if (!GLPlatform::instance()->isGLES()) {
-        s_supportsFramebufferObjects = hasGLVersion(3, 0) || hasGLExtension("GL_ARB_framebuffer_object") || hasGLExtension(QByteArrayLiteral("GL_EXT_framebuffer_object"));
         s_supportsTextureStorage = hasGLVersion(4, 2) || hasGLExtension(QByteArrayLiteral("GL_ARB_texture_storage"));
         s_supportsTextureSwizzle = hasGLVersion(3, 3) || hasGLExtension(QByteArrayLiteral("GL_ARB_texture_swizzle"));
         // see https://www.opengl.org/registry/specs/ARB/texture_rg.txt
@@ -153,7 +151,6 @@ void GLTexturePrivate::initStatic()
         s_supportsARGB32 = true;
         s_supportsUnpack = true;
     } else {
-        s_supportsFramebufferObjects = true;
         s_supportsTextureStorage = hasGLVersion(3, 0) || hasGLExtension(QByteArrayLiteral("GL_EXT_texture_storage"));
         s_supportsTextureSwizzle = hasGLVersion(3, 0);
         // see https://www.khronos.org/registry/gles/extensions/EXT/EXT_texture_rg.txt
@@ -170,7 +167,6 @@ void GLTexturePrivate::initStatic()
 
 void GLTexturePrivate::cleanup()
 {
-    s_supportsFramebufferObjects = false;
     s_supportsARGB32 = false;
     if (s_fbo) {
         glDeleteFramebuffers(1, &s_fbo);
@@ -321,7 +317,7 @@ void GLTexture::bind()
 
 void GLTexture::generateMipmaps()
 {
-    if (d->m_canUseMipmaps && d->s_supportsFramebufferObjects) {
+    if (d->m_canUseMipmaps) {
         glGenerateMipmap(d->m_target);
     }
 }
@@ -423,7 +419,7 @@ GLenum GLTexture::internalFormat() const
 void GLTexture::clear()
 {
     Q_ASSERT(d->m_owning);
-    if (!GLTexturePrivate::s_fbo && GLFramebuffer::supported() && GLPlatform::instance()->driver() != Driver_Catalyst) { // fail. -> bug #323065
+    if (!GLTexturePrivate::s_fbo && GLPlatform::instance()->driver() != Driver_Catalyst) { // fail. -> bug #323065
         glGenFramebuffers(1, &GLTexturePrivate::s_fbo);
     }
 
@@ -553,11 +549,6 @@ QMatrix4x4 GLTexture::matrix(TextureCoordinateType type) const
     return d->m_matrix[type];
 }
 
-bool GLTexture::framebufferObjectSupported()
-{
-    return GLTexturePrivate::s_supportsFramebufferObjects;
-}
-
 bool GLTexture::supportsSwizzle()
 {
     return GLTexturePrivate::s_supportsTextureSwizzle;

src/opengl/gltexture.h

@@ -112,8 +112,6 @@ public:
 
     void generateMipmaps();
 
-    static bool framebufferObjectSupported();
-
     /**
      * Returns true if texture swizzle is supported, and false otherwise
      *

src/opengl/gltexture_p.h

@@ -58,7 +58,6 @@ public:
 
     static void initStatic();
 
-    static bool s_supportsFramebufferObjects;
     static bool s_supportsARGB32;
     static bool s_supportsUnpack;
     static bool s_supportsTextureStorage;

src/opengl/openglcontext.cpp

@@ -119,7 +119,8 @@ bool OpenGlContext::checkSupported() const
     const bool supportsGLSL = m_isOpenglES || (hasOpenglExtension("GL_ARB_shader_objects") && hasOpenglExtension("GL_ARB_fragment_shader") && hasOpenglExtension("GL_ARB_vertex_shader"));
     const bool supportsNonPowerOfTwoTextures = m_isOpenglES || hasOpenglExtension("GL_ARB_texture_non_power_of_two");
     const bool supports3DTextures = !m_isOpenglES || hasVersion(Version(3, 0)) || hasOpenglExtension("GL_OES_texture_3D");
-    return supportsGLSL && supportsNonPowerOfTwoTextures && supports3DTextures;
+    const bool supportsFBOs = m_isOpenglES || hasVersion(Version(3, 0)) || hasOpenglExtension("GL_ARB_framebuffer_object") || hasOpenglExtension(QByteArrayLiteral("GL_EXT_framebuffer_object"));
+    return supportsGLSL && supportsNonPowerOfTwoTextures && supports3DTextures && supportsFBOs;
 }
 
 void OpenGlContext::setShaderManager(ShaderManager *manager)

src/plugins/backgroundcontrast/contrast.cpp

@@ -297,7 +297,7 @@ bool ContrastEffect::enabledByDefault()
 
 bool ContrastEffect::supported()
 {
-    bool supported = effects->isOpenGLCompositing() && GLFramebuffer::supported();
+    bool supported = effects->isOpenGLCompositing();
 
     if (supported) {
         int maxTexSize;

src/plugins/blur/blur.cpp

@@ -371,7 +371,7 @@ bool BlurEffect::enabledByDefault()
 
 bool BlurEffect::supported()
 {
-    return effects->isOpenGLCompositing() && GLFramebuffer::supported() && GLFramebuffer::blitSupported();
+    return effects->isOpenGLCompositing() && GLFramebuffer::blitSupported();
 }
 
 bool BlurEffect::decorationSupportsBlurBehind(const EffectWindow *w) const

src/plugins/screenshot/screenshot.cpp

@@ -85,7 +85,7 @@ static void convertFromGLImage(QImage &img, int w, int h, const OutputTransform
 
 bool ScreenShotEffect::supported()
 {
-    return effects->isOpenGLCompositing() && GLFramebuffer::supported();
+    return effects->isOpenGLCompositing();
 }
 
 ScreenShotEffect::ScreenShotEffect()