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rhi: gl: Support reading back 1 byte texture formats

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The GL texture readback is limited due to the underspecified glReadPixels,
especially on GLES. To preserve our sanity, we just do a GL_RGBA
readback always. This only worked for 4 byte formats, but now we extend
it to handle the 1 byte (R8 and RED_OR_ALPHA8) formats.

Note that this relies on the fact that the GL implementation is able to
do a GL_RGBA readback for a GL_R8 or GL_ALPHA texture.

Change-Id: I8286dca42964f0cbc6645355e105bbd81ec685ca
Reviewed-by: Christian Strømme <christian.stromme@qt.io>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
This commit is contained in:
Laszlo Agocs 2020-06-11 17:40:56 +02:00
parent 03dfd4199d
commit 9d0a15b7a3
1 changed files with 25 additions and 5 deletions
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30
src/gui/rhi/qrhigles2.cpp
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@ -2396,13 +2396,33 @@ void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
result->format = QRhiTexture::RGBA8;
// readPixels handles multisample resolving implicitly
}
result->data.resize(result->pixelSize.width() * result->pixelSize.height() * 4);
const int w = result->pixelSize.width();
const int h = result->pixelSize.height();
if (mipLevel == 0 || caps.nonBaseLevelFramebufferTexture) {
// With GLES (2.0?) GL_RGBA is the only mandated readback format, so stick with it.
f->glReadPixels(0, 0, result->pixelSize.width(), result->pixelSize.height(),
GL_RGBA, GL_UNSIGNED_BYTE,
result->data.data());
// With GLES, GL_RGBA is the only mandated readback format, so stick with it.
if (result->format == QRhiTexture::R8 || result->format == QRhiTexture::RED_OR_ALPHA8) {
result->data.resize(w * h);
QByteArray tmpBuf;
tmpBuf.resize(w * h * 4);
f->glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, tmpBuf.data());
const quint8 *srcBase = reinterpret_cast<const quint8 *>(tmpBuf.constData());
quint8 *dstBase = reinterpret_cast<quint8 *>(result->data.data());
const int componentIndex = isFeatureSupported(QRhi::RedOrAlpha8IsRed) ? 0 : 3;
for (int y = 0; y < h; ++y) {
const quint8 *src = srcBase + y * w * 4;
quint8 *dst = dstBase + y * w;
int count = w;
while (count-- > 0) {
*dst++ = src[componentIndex];
src += 4;
}
}
} else {
result->data.resize(w * h * 4);
f->glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, result->data.data());
}
} else {
result->data.resize(w * h * 4);
result->data.fill('\0');
}
if (fbo) {