rhi: gl: Attempt reading back floating point formats

...in the hope that they may work. If not, that's it, but at least we
tried.

Task-number: QTBUG-76970
Change-Id: I134c5cc4cfb5ad1e6f9edbfcf506df20022e127a
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 17 insertions, 2 deletions

diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index fac05f4947..cd1e4ec944 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -2740,8 +2740,23 @@ void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
                         }
                     }
                 } else {
-                    result->data.resize(w * h * 4);
-                    f->glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, result->data.data());
+                    switch (result->format) {
+                    // For floating point formats try it because this can be
+                    // relevant for some use cases; if it works, then fine, if
+                    // not, there's nothing we can do.
+                    case QRhiTexture::RGBA16F:
+                        result->data.resize(w * h * 8);
+                        f->glReadPixels(0, 0, w, h, GL_RGBA, GL_HALF_FLOAT, result->data.data());
+                        break;
+                    case QRhiTexture::RGBA32F:
+                        result->data.resize(w * h * 16);
+                        f->glReadPixels(0, 0, w, h, GL_RGBA, GL_FLOAT, result->data.data());
+                        break;
+                    default:
+                        result->data.resize(w * h * 4);
+                        f->glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, result->data.data());
+                        break;
+                    }
                 }
             } else {
                 result->data.resize(w * h * 4);