KWin::GLTexture support external textures

Summary:
Currently KWin::GLTexture is a nice wrapper for creating a GL texture
and performing various operations including rendering.

In a pending patch I want to render the FBO from a QQuickScene directly,
where we have an underlying texture already, but it makes sense to
re-use this class for the rendering. A similar need is in haagch's kwin
VR patchset.

This patch adds a constructor to GLTexture that takes an externally
managed texture and provides the relevant useful KWin features.

Test Plan: Used in patch series

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D24206

libkwineffects/kwingltexture.cpp

@@ -239,6 +239,24 @@ GLTexture::GLTexture(GLenum internalFormat, const QSize &size, int levels)
 {
 }
 
+GLTexture::GLTexture(GLuint textureId, GLenum internalFormat, const QSize &size, int levels)
+    : d_ptr(new GLTexturePrivate())
+{
+    Q_D(GLTexture);
+    d->m_foreign = true;
+    d->m_texture = textureId;
+    d->m_target = GL_TEXTURE_2D;
+    d->m_scale.setWidth(1.0 / size.width());
+    d->m_scale.setHeight(1.0 / size.height());
+    d->m_size = size;
+    d->m_canUseMipmaps = levels > 1;
+    d->m_mipLevels = levels;
+    d->m_filter = levels > 1 ? GL_NEAREST_MIPMAP_LINEAR : GL_NEAREST;
+    d->m_internalFormat = internalFormat;
+
+    d->updateMatrix();
+}
+
 GLTexture::~GLTexture()
 {
 }
@@ -261,6 +279,7 @@ GLTexturePrivate::GLTexturePrivate()
  , m_filterChanged(true)
  , m_wrapModeChanged(false)
  , m_immutable(false)
+ , m_foreign(false)
  , m_mipLevels(1)
  , m_unnormalizeActive(0)
  , m_normalizeActive(0)
@@ -272,7 +291,7 @@ GLTexturePrivate::GLTexturePrivate()
 GLTexturePrivate::~GLTexturePrivate()
 {
     delete m_vbo;
-    if (m_texture != 0) {
+    if (m_texture != 0 && !m_foreign) {
         glDeleteTextures(1, &m_texture);
     }
     // Delete the FBO if this is the last Texture
@@ -333,6 +352,7 @@ void GLTexture::update(const QImage &image, const QPoint &offset, const QRect &s
         return;
 
     Q_D(GLTexture);
+    Q_ASSERT(!d->m_foreign);
 
     bool useUnpack = !src.isNull() && d->s_supportsUnpack && d->s_supportsARGB32 && image.format() == QImage::Format_ARGB32_Premultiplied;
 
@@ -510,6 +530,7 @@ GLenum GLTexture::internalFormat() const
 void GLTexture::clear()
 {
     Q_D(GLTexture);
+    Q_ASSERT(!d->m_foreign);
     if (!GLTexturePrivate::s_fbo && GLRenderTarget::supported() &&
         GLPlatform::instance()->driver() != Driver_Catalyst) // fail. -> bug #323065
         glGenFramebuffers(1, &GLTexturePrivate::s_fbo);

libkwineffects/kwingltexture.h

@@ -59,6 +59,13 @@ public:
     explicit GLTexture(const QString& fileName);
     GLTexture(GLenum internalFormat, int width, int height, int levels = 1);
     explicit GLTexture(GLenum internalFormat, const QSize &size, int levels = 1);
+
+    /**
+     * Create a GLTexture wrapper around an existing texture.
+     * Management of the underlying texture remains the responsibility of the caller.
+     * @since 5.18
+     */
+    explicit GLTexture(GLuint textureId, GLenum internalFormat, const QSize &size, int levels = 1);
     virtual ~GLTexture();
 
     GLTexture & operator = (const GLTexture& tex);

libkwineffects/kwingltexture_p.h

@@ -63,6 +63,7 @@ public:
     bool m_filterChanged;
     bool m_wrapModeChanged;
     bool m_immutable;
+    bool m_foreign;
     int m_mipLevels;
 
     int m_unnormalizeActive; // 0 - no, otherwise refcount