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Texture-based thick lines: Allow interpolation between textures for non-integer line widths

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This commit is contained in:
Ben Carter
2020-02-06 14:30:29 +09:00
committed by omar
parent 222b7ddbfa
commit 403bf45245
3 changed files with 55 additions and 37 deletions
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88
imgui_draw.cpp
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@@ -677,11 +677,12 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
const float AA_SIZE = 1.0f;
const ImU32 col_trans = col & ~IM_COL32_A_MASK;
// The -0.5f here is to better match the geometry-based code, and also shift the transition point from one width texture to another off the integer values (where it will be less noticeable)
const int integer_thickness = ImMax((int)(thickness - 0.5f), 1);
// The thick_line test is an attempt to compensate for the way half_draw_size gets calculated later, which special-cases 1.0f width lines
const int integer_thickness = thick_line ? ImMax((int)(thickness), 1) : 2;
const float fractional_thickness = thick_line ? (thickness) - integer_thickness : 0.0f;
// Do we want to draw this line using a texture?
const bool use_texture = (Flags & ImDrawListFlags_AntiAliasedLinesUseTexData) && (integer_thickness <= IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX);
const bool use_texture = (Flags & ImDrawListFlags_AntiAliasedLinesUseTexData) && (integer_thickness < IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX);
// We should never hit this, because NewFrame() doesn't set ImDrawListFlags_AntiAliasedLinesUseTexData unless ImFontAtlasFlags_NoAALines is off
IM_ASSERT_PARANOID((!use_texture) || (!(_Data->Font->ContainerAtlas->Flags & ImFontAtlasFlags_NoAALines)));
@@ -711,8 +712,9 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
// If we are drawing a one-pixel-wide line without a texture, or a textured line of any width, we only need 2 or 3 vertices per point
if (!thick_line || use_texture)
{
// The width of the geometry we need to draw
const float half_draw_size = (!thick_line) ? AA_SIZE : (AA_SIZE + (thickness * 0.5f));
// The width of the geometry we need to draw - this is essentially <thickness> pixels for the line itself, plus one pixel for AA
// We don't use AA_SIZE here because the +1 is tied to the generated texture and so alternate values won't work without changes to that code
const float half_draw_size = (thickness * 0.5f) + 1;
// If line is not closed, the first and last points need to be generated differently as there are no normals to blend
if (!closed)
@@ -770,7 +772,18 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
if (use_texture)
{
// If we're using textures we only need to emit the left/right edge vertices
const ImVec4 tex_uvs = (*_Data->TexUvAALines)[integer_thickness - 1];
ImVec4 tex_uvs;
if (fractional_thickness == 0.0f) // Fast path for pure integer widths
tex_uvs = (*_Data->TexUvAALines)[integer_thickness];
else
{
// Calculate UV by interpolating between the two nearest integer line widths
const ImVec4 tex_uvs_0 = (*_Data->TexUvAALines)[integer_thickness];
const ImVec4 tex_uvs_1 = (*_Data->TexUvAALines)[integer_thickness + 1];
tex_uvs = ImLerp(tex_uvs_0, tex_uvs_1, fractional_thickness);
}
for (int i = 0; i < points_count; i++)
{
@@ -2373,24 +2386,14 @@ static void ImFontAtlasBuildRenderDefaultTexData(ImFontAtlas* atlas)
atlas->TexUvWhitePixel = ImVec2((r->X + 0.5f) * atlas->TexUvScale.x, (r->Y + 0.5f) * atlas->TexUvScale.y);
}
// This is called/shared by both the stb_truetype and the FreeType builder.
const unsigned int FONT_ATLAS_AA_LINE_TEX_HEIGHT = 1; // Technically we only need 1 pixel in the ideal case but this can be increased if necessary to give a border to avoid sampling artifacts
static void ImFontAtlasBuildRegisterAALineCustomRects(ImFontAtlas* atlas)
{
if (atlas->AALineRectIds.Size > 0)
return;
if ((atlas->Flags & ImFontAtlasFlags_NoAALines))
return;
for (int n = 0; n < IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX; n++)
{
// The "width + 3" here is interesting. +2 is to give space for the end caps, but the remaining +1 is
// because (empirically) to match the behavior of the untextured render path we need to draw lines one pixel wider.
const int width = n + 1; // The line width this entry corresponds to
atlas->AALineRectIds.push_back(atlas->AddCustomRectRegular(width + 3, FONT_ATLAS_AA_LINE_TEX_HEIGHT));
}
const int max_width = IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX; // The maximum line width we want to generate
// The "max_width + 2" here is to give space for the end caps, whilst height (IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX+1) is to accommodate the fact we have a zero-width row
atlas->AALineRectId = atlas->AddCustomRectRegular(max_width + 2, IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX + 1);
}
static void ImFontAtlasBuildRenderAALinesTexData(ImFontAtlas* atlas)
@@ -2401,27 +2404,42 @@ static void ImFontAtlasBuildRenderAALinesTexData(ImFontAtlas* atlas)
if (atlas->Flags & ImFontAtlasFlags_NoAALines)
return;
const int w = atlas->TexWidth;
for (unsigned int n = 0; n < IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX; n++)
{
IM_ASSERT(atlas->AALineRectIds.Size > (int)n);
ImFontAtlasCustomRect& r = atlas->CustomRects[atlas->AALineRectIds[n]];
IM_ASSERT(r.IsPacked());
ImFontAtlasCustomRect& r = atlas->CustomRects[atlas->AALineRectId];
IM_ASSERT(r.IsPacked());
// We fill as many lines as we were given, to allow for >1 lines being used to work around sampling weirdness
for (unsigned int y = 0; y < r.Height; y++)
{
// Each line consists of two empty pixels at the ends, with a line of solid pixels in the middle
unsigned char* write_ptr = &atlas->TexPixelsAlpha8[r.X + ((r.Y + y) * w)];
// This generates a triangular shape in the texture, with the various line widths stacked on top of each other to allow interpolation between them
const int w = atlas->TexWidth;
for (unsigned int n = 0; n < (IM_DRAWLIST_TEX_AA_LINES_WIDTH_MAX + 1); n++) // +1 because of the zero-width row
{
unsigned int y = n;
unsigned int line_width = n;
// Each line consists of at least two empty pixels at the ends, with a line of solid pixels in the middle
unsigned int pad_left = (r.Width - line_width) / 2;
unsigned int pad_right = r.Width - (pad_left + line_width);
// Make sure we're inside the texture bounds before we start writing pixels
IM_ASSERT_PARANOID(pad_left + line_width + pad_right == r.Width);
IM_ASSERT_PARANOID(y < r.Height);
// Write each slice
unsigned char* write_ptr = &atlas->TexPixelsAlpha8[r.X + ((r.Y + y) * w)];
for (unsigned int x = 0; x < pad_left; x++)
*(write_ptr++) = 0;
for (unsigned short x = 0; x < (r.Width - 2U); x++)
*(write_ptr++) = 0xFF;
for (unsigned int x = 0; x < line_width; x++)
*(write_ptr++) = 0xFF;
for (unsigned int x = 0; x < pad_right; x++)
*(write_ptr++) = 0;
}
// Calculate UVs for this line
ImFontAtlasCustomRect line_rect = r;
line_rect.X += (unsigned short)(pad_left - 1);
line_rect.Width = (unsigned short)(line_width + 2);
line_rect.Y += (unsigned short)y;
line_rect.Height = 1;
ImVec2 uv0, uv1;
atlas->CalcCustomRectUV(&r, &uv0, &uv1);
float halfV = (uv0.y + uv1.y) * 0.5f; // Calculate a constant V in the middle of the texture as we want a horizontal slice (with some padding either side to avoid sampling artifacts)
atlas->CalcCustomRectUV(&line_rect, &uv0, &uv1);
float halfV = (uv0.y + uv1.y) * 0.5f; // Calculate a constant V in the middle of the row to avoid sampling artifacts
atlas->TexUvAALines.push_back(ImVec4(uv0.x, halfV, uv1.x, halfV));
}
}