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Commit 66ba1f99 by Nicolas Capens Committed by Nicolas Capens
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Rasterize 'Bresenham' line segments as parallelograms

The previous 'connected diamonds' polygon that was used to rasterize Bresenham lines suffered from duplicate rasterization of endpoints, which violates the diamond exit-rule and is disallowed by the Vulkan (and OpenGL) spec. This change rasterizes Bresenham lines as a parallelogram, as described by Vulkan's non-strictLines algorithm. This satisfied Vulkan's requirements laid out in section 26.10.2 Bresenham Line Segment Rasterization: "Implementations may use other line segment rasterization algorithms, subject to the following rules: - The coordinates of a fragment produced by the algorithm must not deviate by more than one unit in either x or y framebuffer coordinates from a corresponding fragment produced by the diamond- exit rule. - The total number of fragments produced by the algorithm must not differ from that produced by the diamond-exit rule by no more than one. - For an x-major line, two fragments that lie in the same framebuffer- coordinate column must not be produced (for a y-major line, two fragments that lie in the same framebuffer-coordinate row must not be produced). - If two line segments share a common endpoint, and both segments are either x-major (both left-to-right or both right-to-left) or y-mayor (both bottom-to-top or both top-to-bottom), then rasterizing both segments must not produce duplicate fragments. Fragments also must not be omitted so as to interrupt continuity of the connected segments." OpenGL ES line rasterization has not been modified as part of this change, to not require rebasing of golden images, but the parallelogram algorithm was made available for easy comparison. Bug: b/80135519 Change-Id: I09e8b90a393d3a08387d79669d9dbe5f83a0811d Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38049 Presubmit-Ready: Nicolas Capens <nicolascapens@google.com> Kokoro-Presubmit: kokoro <noreply+kokoro@google.com> Tested-by: 's avatarNicolas Capens <nicolascapens@google.com> Reviewed-by: 's avatarChris Forbes <chrisforbes@google.com> Reviewed-by: 's avatarAlexis Hétu <sugoi@google.com>
parent 90df527f
Showing with 206 additions and 11 deletions
src/Device/Renderer.cpp
...@@ -814,16 +814,17 @@ namespace sw ...@@ -814,16 +814,17 @@ namespace sw
return false; return false;
} }
// TODO(b/142965928): Bresenham lines should render the same with or without // We use rectangular lines for non-Bresenham lines (cf. 'strictLines'),
// multisampling, which will require a special case in the // and for Bresenham lines when multiSampling is enabled.
// code when multisampling is on. For now, we just use // FIXME(b/142965928): Bresenham lines should render the same with or without
// rectangular lines when multisampling is enabled. // multisampling, which will require a special case in the
// code when multisampling is on. For now, we just use
// We use rectangular lines for non Bresenham lines and // rectangular lines when multisampling is enabled.
// for Bresenham lines when multiSampling is enabled
if((draw.setupState.multiSample > 1) || if((draw.setupState.multiSample > 1) ||
(draw.lineRasterizationMode != VK_LINE_RASTERIZATION_MODE_BRESENHAM_EXT)) // Rectangle centered on the line segment (draw.lineRasterizationMode != VK_LINE_RASTERIZATION_MODE_BRESENHAM_EXT))
{ {
// Rectangle centered on the line segment
float4 P[4]; float4 P[4];
int C[4]; int C[4];
...@@ -876,8 +877,13 @@ namespace sw ...@@ -876,8 +877,13 @@ namespace sw
return draw.setupRoutine(&primitive, &triangle, &polygon, &data); return draw.setupRoutine(&primitive, &triangle, &polygon, &data);
} }
} }
else // Diamond test convention else if(false) // TODO(b/80135519): Deprecate
{ {
// Connecting diamonds polygon
// This shape satisfies the diamond test convention, except for the exit rule part.
// Line segments with overlapping endpoints have duplicate fragments.
// The ideal algorithm requires half-open line rasterization (b/80135519).
float4 P[8]; float4 P[8];
int C[8]; int C[8];
...@@ -982,6 +988,97 @@ namespace sw ...@@ -982,6 +988,97 @@ namespace sw
return draw.setupRoutine(&primitive, &triangle, &polygon, &data); return draw.setupRoutine(&primitive, &triangle, &polygon, &data);
} }
} }
else
{
// Parallelogram approximating Bresenham line
// This algorithm does not satisfy the ideal diamond-exit rule, but does avoid the
// duplicate fragment rasterization problem and satisfies all of Vulkan's minimum
// requirements for Bresenham line segment rasterization.
float4 P[8];
P[0] = P0;
P[1] = P0;
P[2] = P0;
P[3] = P0;
P[4] = P1;
P[5] = P1;
P[6] = P1;
P[7] = P1;
float dx0 = lineWidth * 0.5f * P0.w / W;
float dy0 = lineWidth * 0.5f * P0.w / H;
float dx1 = lineWidth * 0.5f * P1.w / W;
float dy1 = lineWidth * 0.5f * P1.w / H;
P[0].x += -dx0;
P[1].y += +dy0;
P[2].x += +dx0;
P[3].y += -dy0;
P[4].x += -dx1;
P[5].y += +dy1;
P[6].x += +dx1;
P[7].y += -dy1;
float4 L[4];
if(dx > -dy)
{
if(dx > dy) // Right
{
L[0] = P[1];
L[1] = P[5];
L[2] = P[7];
L[3] = P[3];
}
else // Down
{
L[0] = P[0];
L[1] = P[4];
L[2] = P[6];
L[3] = P[2];
}
}
else
{
if(dx > dy) // Up
{
L[0] = P[0];
L[1] = P[2];
L[2] = P[6];
L[3] = P[4];
}
else // Left
{
L[0] = P[1];
L[1] = P[3];
L[2] = P[7];
L[3] = P[5];
}
}
int C0 = Clipper::ComputeClipFlags(L[0]);
int C1 = Clipper::ComputeClipFlags(L[1]);
int C2 = Clipper::ComputeClipFlags(L[2]);
int C3 = Clipper::ComputeClipFlags(L[3]);
if((C0 & C1 & C2 & C3) == Clipper::CLIP_FINITE)
{
Polygon polygon(L, 4);
int clipFlagsOr = C0 | C1 | C2 | C3;
if(clipFlagsOr != Clipper::CLIP_FINITE)
{
if(!Clipper::Clip(polygon, clipFlagsOr, draw))
{
return false;
}
}
return draw.setupRoutine(&primitive, &triangle, &polygon, &data);
}
}
return false; return false;
} }
......
src/Renderer/Renderer.cpp
...@@ -1790,8 +1790,10 @@ namespace sw ...@@ -1790,8 +1790,10 @@ namespace sw
return false; return false;
} }
if(state.multiSample > 1) // Rectangle if(state.multiSample > 1)
{ {
// Rectangle centered on the line segment
float4 P[4]; float4 P[4];
int C[4]; int C[4];
...@@ -1844,8 +1846,13 @@ namespace sw ...@@ -1844,8 +1846,13 @@ namespace sw
return setupRoutine(&primitive, &triangle, &polygon, &data); return setupRoutine(&primitive, &triangle, &polygon, &data);
} }
} }
else // Diamond test convention else if(true)
{ {
// Connecting diamonds polygon
// This shape satisfies the diamond test convention, except for the exit rule part.
// Line segments with overlapping endpoints have duplicate fragments.
// The ideal algorithm requires half-open line rasterization (b/80135519).
float4 P[8]; float4 P[8];
int C[8]; int C[8];
...@@ -1950,6 +1957,97 @@ namespace sw ...@@ -1950,6 +1957,97 @@ namespace sw
return setupRoutine(&primitive, &triangle, &polygon, &data); return setupRoutine(&primitive, &triangle, &polygon, &data);
} }
} }
else
{
// Parallelogram approximating Bresenham line
// This algorithm does not satisfy the ideal diamond-exit rule, but does avoid the
// duplicate fragment rasterization problem and satisfies all of Vulkan's minimum
// requirements for Bresenham line segment rasterization.
float4 P[8];
P[0] = P0;
P[1] = P0;
P[2] = P0;
P[3] = P0;
P[4] = P1;
P[5] = P1;
P[6] = P1;
P[7] = P1;
float dx0 = lineWidth * 0.5f * P0.w / W;
float dy0 = lineWidth * 0.5f * P0.w / H;
float dx1 = lineWidth * 0.5f * P1.w / W;
float dy1 = lineWidth * 0.5f * P1.w / H;
P[0].x += -dx0;
P[1].y += +dy0;
P[2].x += +dx0;
P[3].y += -dy0;
P[4].x += -dx1;
P[5].y += +dy1;
P[6].x += +dx1;
P[7].y += -dy1;
float4 L[4];
if(dx > -dy)
{
if(dx > dy) // Right
{
L[0] = P[1];
L[1] = P[5];
L[2] = P[7];
L[3] = P[3];
}
else // Down
{
L[0] = P[0];
L[1] = P[4];
L[2] = P[6];
L[3] = P[2];
}
}
else
{
if(dx > dy) // Up
{
L[0] = P[0];
L[1] = P[2];
L[2] = P[6];
L[3] = P[4];
}
else // Left
{
L[0] = P[1];
L[1] = P[3];
L[2] = P[7];
L[3] = P[5];
}
}
int C0 = clipper->computeClipFlags(L[0]);
int C1 = clipper->computeClipFlags(L[1]);
int C2 = clipper->computeClipFlags(L[2]);
int C3 = clipper->computeClipFlags(L[3]);
if((C0 & C1 & C2 & C3) == Clipper::CLIP_FINITE)
{
Polygon polygon(L, 4);
int clipFlagsOr = C0 | C1 | C2 | C3;
if(clipFlagsOr != Clipper::CLIP_FINITE)
{
if(!clipper->clip(polygon, clipFlagsOr, draw))
{
return false;
}
}
return setupRoutine(&primitive, &triangle, &polygon, &data);
}
}
return false; return false;
} }
......
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