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Use bilinear interpolation to compute texture coords of subquads

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On Wayland, a surface must be displayed the same way no matter how the
attached buffer is transformed. In order to guarantee that, we build the
surface-to-buffer matrix, which is used to compute the texture coords.

The surface-to-buffer matrix represents an affine transformation. Thus,
performing linear interpolation between texture coordinates won't end up
in corrupted rendered results. This is the main assumption that we make
during generation of contents window quads. After creating a sub-quad,
the new quad's texture coordinates are computed by interpolating between
the source quad's texture coords.

However, WindowQuad::makeSubQuad() makes a concrete assumption about the
order of texture coords, which might be false if the attached wayland
buffer is rotated 90 or 270 degrees.

This issue went unnoticed after merging the viewporter patches because
the developer who was working on it had been using primarily nested
kwin_wayland for testing purposes. And it appears like kwin schedules
full screen repaints even though it supports buffer age. It still needs
some investigation why that happens.

BUG: 428003
This commit is contained in:
Vlad Zahorodnii 2020-10-20 11:16:31 +03:00
parent 5e037570fe
commit 7301564e4f
2 changed files with 35 additions and 41 deletions
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16
autotests/libkwineffects/windowquadlisttest.cpp
View file

@ -98,12 +98,12 @@ void WindowQuadListTest::testMakeGrid()
const KWin::WindowVertex &expectedVertex = expectedQuad[index];
if (actualVertex.x() != expectedVertex.x()) return false;
if (actualVertex.y() != expectedVertex.y()) return false;
if (actualVertex.u() != expectedVertex.u()) return false;
if (actualVertex.v() != expectedVertex.v()) return false;
if (!qFuzzyIsNull(actualVertex.u() - expectedVertex.u())) return false;
if (!qFuzzyIsNull(actualVertex.v() - expectedVertex.v())) return false;
if (actualVertex.originalX() != expectedVertex.originalX()) return false;
if (actualVertex.originalY() != expectedVertex.originalY()) return false;
if (actualVertex.textureX() != expectedVertex.textureX()) return false;
if (actualVertex.textureY() != expectedVertex.textureY()) return false;
if (!qFuzzyIsNull(actualVertex.textureX() - expectedVertex.textureX())) return false;
if (!qFuzzyIsNull(actualVertex.textureY() - expectedVertex.textureY())) return false;
return true;
};
found = vertexTest(0) && vertexTest(1) && vertexTest(2) && vertexTest(3);
@ -185,12 +185,12 @@ void WindowQuadListTest::testMakeRegularGrid()
const KWin::WindowVertex &expectedVertex = expectedQuad[index];
if (actualVertex.x() != expectedVertex.x()) return false;
if (actualVertex.y() != expectedVertex.y()) return false;
if (actualVertex.u() != expectedVertex.u()) return false;
if (actualVertex.v() != expectedVertex.v()) return false;
if (!qFuzzyIsNull(actualVertex.u() - expectedVertex.u())) return false;
if (!qFuzzyIsNull(actualVertex.v() - expectedVertex.v())) return false;
if (actualVertex.originalX() != expectedVertex.originalX()) return false;
if (actualVertex.originalY() != expectedVertex.originalY()) return false;
if (actualVertex.textureX() != expectedVertex.textureX()) return false;
if (actualVertex.textureY() != expectedVertex.textureY()) return false;
if (!qFuzzyIsNull(actualVertex.textureX() - expectedVertex.textureX())) return false;
if (!qFuzzyIsNull(actualVertex.textureY() - expectedVertex.textureY())) return false;
return true;
};
found = vertexTest(0) && vertexTest(1) && vertexTest(2) && vertexTest(3);

60
libkwineffects/kwineffects.cpp
View file

@ -866,45 +866,39 @@ WindowQuad WindowQuad::makeSubQuad(double x1, double y1, double x2, double y2) c
ret.verts[ 2 ].oy = y2;
ret.verts[ 3 ].oy = y2;
const double my_u0 = verts[0].tx;
const double my_u1 = verts[2].tx;
const double my_v0 = verts[0].ty;
const double my_v1 = verts[2].ty;
const double xOrigin = left();
const double yOrigin = top();
const double width = right() - left();
const double height = bottom() - top();
const double texWidth = my_u1 - my_u0;
const double texHeight = my_v1 - my_v0;
const double widthReciprocal = 1 / (right() - xOrigin);
const double heightReciprocal = 1 / (bottom() - yOrigin);
if (!uvAxisSwapped()) {
const double u0 = (x1 - left()) / width * texWidth + my_u0;
const double u1 = (x2 - left()) / width * texWidth + my_u0;
const double v0 = (y1 - top()) / height * texHeight + my_v0;
const double v1 = (y2 - top()) / height * texHeight + my_v0;
for (int i = 0; i < 4; ++i) {
const double w1 = (ret.verts[i].px - xOrigin) * widthReciprocal;
const double w2 = (ret.verts[i].py - yOrigin) * heightReciprocal;
ret.verts[0].tx = u0;
ret.verts[3].tx = u0;
ret.verts[1].tx = u1;
ret.verts[2].tx = u1;
ret.verts[0].ty = v0;
ret.verts[1].ty = v0;
ret.verts[2].ty = v1;
ret.verts[3].ty = v1;
// Use bilinear interpolation to compute the texture coords.
ret.verts[i].tx = (1 - w1) * (1 - w2) * verts[0].tx +
w1 * (1 - w2) * verts[1].tx +
w1 * w2 * verts[2].tx + (1 - w1) * w2 * verts[3].tx;
ret.verts[i].ty = (1 - w1) * (1 - w2) * verts[0].ty +
w1 * (1 - w2) * verts[1].ty +
w1 * w2 * verts[2].ty + (1 - w1) * w2 * verts[3].ty;
}
} else {
const double u0 = (y1 - top()) / height * texWidth + my_u0;
const double u1 = (y2 - top()) / height * texWidth + my_u0;
const double v0 = (x1 - left()) / width * texHeight + my_v0;
const double v1 = (x2 - left()) / width * texHeight + my_v0;
// Same as above, with just verts[1] and verts[3] being swapped.
for (int i = 0; i < 4; ++i) {
const double w1 = (ret.verts[i].py - yOrigin) * heightReciprocal;
const double w2 = (ret.verts[i].px - xOrigin) * widthReciprocal;
ret.verts[0].tx = u0;
ret.verts[1].tx = u0;
ret.verts[2].tx = u1;
ret.verts[3].tx = u1;
ret.verts[0].ty = v0;
ret.verts[3].ty = v0;
ret.verts[1].ty = v1;
ret.verts[2].ty = v1;
// Use bilinear interpolation to compute the texture coords.
ret.verts[i].tx = (1 - w1) * (1 - w2) * verts[0].tx +
w1 * (1 - w2) * verts[3].tx +
w1 * w2 * verts[2].tx + (1 - w1) * w2 * verts[1].tx;
ret.verts[i].ty = (1 - w1) * (1 - w2) * verts[0].ty +
w1 * (1 - w2) * verts[3].ty +
w1 * w2 * verts[2].ty + (1 - w1) * w2 * verts[1].ty;
}
}
ret.setUVAxisSwapped(uvAxisSwapped());