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ImDrawList: Store header/current ImDrawCmd in instance to simplify me…
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…rging code. Amend 0320e72, toward #3163, #3129
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@ocornut
ocornut committed Jun 8, 2020
1 parent 57191fe commit a6bb047
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Showing 2 changed files with 57 additions and 61 deletions.
16 changes: 9 additions & 7 deletions imgui.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1874,19 +1874,21 @@ typedef void (*ImDrawCallback)(const ImDrawList* parent_list, const ImDrawCmd* c
#define ImDrawCallback_ResetRenderState (ImDrawCallback)(-1)

// Typically, 1 command = 1 GPU draw call (unless command is a callback)
// Pre 1.71 back-ends will typically ignore the VtxOffset/IdxOffset fields. When 'io.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset'
// is enabled, those fields allow us to render meshes larger than 64K vertices while keeping 16-bit indices.
// - VtxOffset/IdxOffset: When 'io.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset' is enabled,
// those fields allow us to render meshes larger than 64K vertices while keeping 16-bit indices.
// Pre-1.71 back-ends will typically ignore the VtxOffset/IdxOffset fields.
// - The ClipRect/TextureId/VtxOffset fields must be contiguous as we memcmp() them together (this is asserted for).
struct ImDrawCmd
{
unsigned int ElemCount; // 4 // Number of indices (multiple of 3) to be rendered as triangles. Vertices are stored in the callee ImDrawList's vtx_buffer[] array, indices in idx_buffer[].
ImVec4 ClipRect; // 4*4 // Clipping rectangle (x1, y1, x2, y2). Subtract ImDrawData->DisplayPos to get clipping rectangle in "viewport" coordinates
ImTextureID TextureId; // 4-8 // User-provided texture ID. Set by user in ImfontAtlas::SetTexID() for fonts or passed to Image*() functions. Ignore if never using images or multiple fonts atlas.
unsigned int VtxOffset; // 4 // Start offset in vertex buffer. Pre-1.71 or without ImGuiBackendFlags_RendererHasVtxOffset: always 0. With ImGuiBackendFlags_RendererHasVtxOffset: may be >0 to support meshes larger than 64K vertices with 16-bit indices.
unsigned int VtxOffset; // 4 // Start offset in vertex buffer. ImGuiBackendFlags_RendererHasVtxOffset: always 0, otherwise may be >0 to support meshes larger than 64K vertices with 16-bit indices.
unsigned int IdxOffset; // 4 // Start offset in index buffer. Always equal to sum of ElemCount drawn so far.
unsigned int ElemCount; // 4 // Number of indices (multiple of 3) to be rendered as triangles. Vertices are stored in the callee ImDrawList's vtx_buffer[] array, indices in idx_buffer[].
ImDrawCallback UserCallback; // 4-8 // If != NULL, call the function instead of rendering the vertices. clip_rect and texture_id will be set normally.
void* UserCallbackData; // 4-8 // The draw callback code can access this.

ImDrawCmd() { ElemCount = 0; TextureId = (ImTextureID)NULL; VtxOffset = IdxOffset = 0; UserCallback = NULL; UserCallbackData = NULL; }
ImDrawCmd() { memset(this, 0, sizeof(*this)); } // Also ensure our padding fields are zeroed
};

// Vertex index, default to 16-bit
Expand Down Expand Up @@ -1977,17 +1979,17 @@ struct ImDrawList
// [Internal, used while building lists]
const ImDrawListSharedData* _Data; // Pointer to shared draw data (you can use ImGui::GetDrawListSharedData() to get the one from current ImGui context)
const char* _OwnerName; // Pointer to owner window's name for debugging
unsigned int _VtxCurrentOffset; // [Internal] Always 0 unless 'Flags & ImDrawListFlags_AllowVtxOffset'.
unsigned int _VtxCurrentIdx; // [Internal] Generally == VtxBuffer.Size unless we are past 64K vertices, in which case this gets reset to 0.
ImDrawVert* _VtxWritePtr; // [Internal] point within VtxBuffer.Data after each add command (to avoid using the ImVector<> operators too much)
ImDrawIdx* _IdxWritePtr; // [Internal] point within IdxBuffer.Data after each add command (to avoid using the ImVector<> operators too much)
ImVector<ImVec4> _ClipRectStack; // [Internal]
ImVector<ImTextureID> _TextureIdStack; // [Internal]
ImVector<ImVec2> _Path; // [Internal] current path building
ImDrawCmd _CmdHeader; // [Internal] Template of active commands. Fields should match those of CmdBuffer.back().
ImDrawListSplitter _Splitter; // [Internal] for channels api (note: prefer using your own persistent instance of ImDrawListSplitter!)

// If you want to create ImDrawList instances, pass them ImGui::GetDrawListSharedData() or create and use your own ImDrawListSharedData (so you can use ImDrawList without ImGui)
ImDrawList(const ImDrawListSharedData* shared_data) { _Data = shared_data; Flags = ImDrawListFlags_None; _VtxCurrentOffset = _VtxCurrentIdx = 0; _VtxWritePtr = NULL; _IdxWritePtr = NULL; _OwnerName = NULL; }
ImDrawList(const ImDrawListSharedData* shared_data) { _Data = shared_data; Flags = ImDrawListFlags_None; _VtxCurrentIdx = 0; _VtxWritePtr = NULL; _IdxWritePtr = NULL; _OwnerName = NULL; }

~ImDrawList() { ClearFreeMemory(); }
IMGUI_API void PushClipRect(ImVec2 clip_rect_min, ImVec2 clip_rect_max, bool intersect_with_current_clip_rect = false); // Render-level scissoring. This is passed down to your render function but not used for CPU-side coarse clipping. Prefer using higher-level ImGui::PushClipRect() to affect logic (hit-testing and widget culling)
Expand Down
102 changes: 48 additions & 54 deletions imgui_draw.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -379,11 +379,17 @@ void ImDrawListSharedData::SetCircleSegmentMaxError(float max_error)
// Initialize before use in a new frame. We always have a command ready in the buffer.
void ImDrawList::ResetForNewFrame()
{
// Verify that the ImDrawCmd fields we want to memcmp() are contiguous in memory.
// (those should be IM_STATIC_ASSERT() in theory but with our pre C++11 setup the whole check doesn't compile with GCC)
IM_ASSERT(IM_OFFSETOF(ImDrawCmd, ClipRect) == 0);
IM_ASSERT(IM_OFFSETOF(ImDrawCmd, TextureId) == sizeof(ImVec4));
IM_ASSERT(IM_OFFSETOF(ImDrawCmd, VtxOffset) == sizeof(ImVec4) + sizeof(ImTextureID));

CmdBuffer.resize(0);
IdxBuffer.resize(0);
VtxBuffer.resize(0);
Flags = _Data->InitialFlags;
_VtxCurrentOffset = 0;
memset(&_CmdHeader, 0, sizeof(_CmdHeader));
_VtxCurrentIdx = 0;
_VtxWritePtr = NULL;
_IdxWritePtr = NULL;
Expand All @@ -400,7 +406,6 @@ void ImDrawList::ClearFreeMemory()
IdxBuffer.clear();
VtxBuffer.clear();
Flags = ImDrawListFlags_None;
_VtxCurrentOffset = 0;
_VtxCurrentIdx = 0;
_VtxWritePtr = NULL;
_IdxWritePtr = NULL;
Expand All @@ -420,16 +425,12 @@ ImDrawList* ImDrawList::CloneOutput() const
return dst;
}

// Using macros because C++ is a terrible language, we want guaranteed inline, no code in header, and no overhead in Debug builds
#define GetCurrentClipRect() (_ClipRectStack.Size ? _ClipRectStack.Data[_ClipRectStack.Size-1] : _Data->ClipRectFullscreen)
#define GetCurrentTextureId() (_TextureIdStack.Size ? _TextureIdStack.Data[_TextureIdStack.Size-1] : (ImTextureID)NULL)

void ImDrawList::AddDrawCmd()
{
ImDrawCmd draw_cmd;
draw_cmd.ClipRect = GetCurrentClipRect();
draw_cmd.TextureId = GetCurrentTextureId();
draw_cmd.VtxOffset = _VtxCurrentOffset;
draw_cmd.ClipRect = _CmdHeader.ClipRect; // Same as calling ImDrawCmd_HeaderCopy()
draw_cmd.TextureId = _CmdHeader.TextureId;
draw_cmd.VtxOffset = _CmdHeader.VtxOffset;
draw_cmd.IdxOffset = IdxBuffer.Size;

IM_ASSERT(draw_cmd.ClipRect.x <= draw_cmd.ClipRect.z && draw_cmd.ClipRect.y <= draw_cmd.ClipRect.w);
Expand All @@ -450,68 +451,62 @@ void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
AddDrawCmd(); // Force a new command after us (see comment below)
}

// Compare ClipRect, TextureId and VtxOffset with a single memcmp()
#define ImDrawCmd_HeaderSize (IM_OFFSETOF(ImDrawCmd, VtxOffset) + sizeof(unsigned int))
#define ImDrawCmd_HeaderCompare(CMD_LHS, CMD_RHS) (memcmp(CMD_LHS, CMD_RHS, ImDrawCmd_HeaderSize)) // Compare ClipRect, TextureId, VtxOffset
#define ImDrawCmd_HeaderCopy(CMD_DST, CMD_SRC) (memcpy(CMD_DST, CMD_SRC, ImDrawCmd_HeaderSize)) // Copy ClipRect, TextureId, VtxOffset

// Our scheme may appears a bit unusual, basically we want the most-common calls AddLine AddRect etc. to not have to perform any check so we always have a command ready in the stack.
// The cost of figuring out if a new command has to be added or if we can merge is paid in those Update** functions only.
void ImDrawList::UpdateClipRect()
{
// If current command is used with different settings we need to add a new command
const ImVec4 curr_clip_rect = GetCurrentClipRect();
ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
if ((curr_cmd->ElemCount != 0 && memcmp(&curr_cmd->ClipRect, &curr_clip_rect, sizeof(ImVec4)) != 0) || curr_cmd->UserCallback != NULL)
if ((curr_cmd->ElemCount != 0 && memcmp(&curr_cmd->ClipRect, &_CmdHeader.ClipRect, sizeof(ImVec4)) != 0) || curr_cmd->UserCallback != NULL)
{
AddDrawCmd();
return;
}

// Try to merge with previous command if it matches, else use current command
if (curr_cmd->ElemCount == 0 && CmdBuffer.Size > 1)
ImDrawCmd* prev_cmd = curr_cmd - 1;
if (curr_cmd->ElemCount == 0 && CmdBuffer.Size > 1 && ImDrawCmd_HeaderCompare(&_CmdHeader, prev_cmd) == 0 && prev_cmd->UserCallback == NULL)
{
ImDrawCmd* prev_cmd = curr_cmd - 1;
if (memcmp(&prev_cmd->ClipRect, &curr_clip_rect, sizeof(ImVec4)) == 0 && prev_cmd->VtxOffset == _VtxCurrentOffset && prev_cmd->TextureId == GetCurrentTextureId() && prev_cmd->UserCallback == NULL)
{
CmdBuffer.pop_back();
return;
}
CmdBuffer.pop_back();
return;
}

curr_cmd->ClipRect = curr_clip_rect;
curr_cmd->ClipRect = _CmdHeader.ClipRect;
}

void ImDrawList::UpdateTextureID()
{
// If current command is used with different settings we need to add a new command
const ImTextureID curr_texture_id = GetCurrentTextureId();
ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
if ((curr_cmd->ElemCount != 0 && curr_cmd->TextureId != curr_texture_id) || curr_cmd->UserCallback != NULL)
if ((curr_cmd->ElemCount != 0 && curr_cmd->TextureId != _CmdHeader.TextureId) || curr_cmd->UserCallback != NULL)
{
AddDrawCmd();
return;
}

// Try to merge with previous command if it matches, else use current command
if (curr_cmd->ElemCount == 0 && CmdBuffer.Size > 1)
ImDrawCmd* prev_cmd = curr_cmd - 1;
if (curr_cmd->ElemCount == 0 && CmdBuffer.Size > 1 && ImDrawCmd_HeaderCompare(&_CmdHeader, prev_cmd) == 0 && prev_cmd->UserCallback == NULL)
{
ImDrawCmd* prev_cmd = curr_cmd - 1;
if (prev_cmd->TextureId == curr_texture_id && memcmp(&prev_cmd->ClipRect, &GetCurrentClipRect(), sizeof(ImVec4)) == 0 && prev_cmd->VtxOffset == _VtxCurrentOffset && prev_cmd->UserCallback == NULL)
{
CmdBuffer.pop_back();
return;
}
CmdBuffer.pop_back();
return;
}

curr_cmd->TextureId = curr_texture_id;
curr_cmd->TextureId = _CmdHeader.TextureId;
}

#undef GetCurrentClipRect
#undef GetCurrentTextureId

// Render-level scissoring. This is passed down to your render function but not used for CPU-side coarse clipping. Prefer using higher-level ImGui::PushClipRect() to affect logic (hit-testing and widget culling)
void ImDrawList::PushClipRect(ImVec2 cr_min, ImVec2 cr_max, bool intersect_with_current_clip_rect)
{
ImVec4 cr(cr_min.x, cr_min.y, cr_max.x, cr_max.y);
if (intersect_with_current_clip_rect && _ClipRectStack.Size)
if (intersect_with_current_clip_rect)
{
ImVec4 current = _ClipRectStack.Data[_ClipRectStack.Size-1];
ImVec4 current = _CmdHeader.ClipRect;
if (cr.x < current.x) cr.x = current.x;
if (cr.y < current.y) cr.y = current.y;
if (cr.z > current.z) cr.z = current.z;
Expand All @@ -521,6 +516,7 @@ void ImDrawList::PushClipRect(ImVec2 cr_min, ImVec2 cr_max, bool intersect_with_
cr.w = ImMax(cr.y, cr.w);

_ClipRectStack.push_back(cr);
_CmdHeader.ClipRect = cr;
UpdateClipRect();
}

Expand All @@ -531,21 +527,22 @@ void ImDrawList::PushClipRectFullScreen()

void ImDrawList::PopClipRect()
{
IM_ASSERT(_ClipRectStack.Size > 0);
_ClipRectStack.pop_back();
_CmdHeader.ClipRect = (_ClipRectStack.Size == 0) ? _Data->ClipRectFullscreen : _ClipRectStack.Data[_ClipRectStack.Size - 1];
UpdateClipRect();
}

void ImDrawList::PushTextureID(ImTextureID texture_id)
{
_TextureIdStack.push_back(texture_id);
_CmdHeader.TextureId = texture_id;
UpdateTextureID();
}

void ImDrawList::PopTextureID()
{
IM_ASSERT(_TextureIdStack.Size > 0);
_TextureIdStack.pop_back();
_CmdHeader.TextureId = (_TextureIdStack.Size == 0) ? (ImTextureID)NULL : _TextureIdStack.Data[_TextureIdStack.Size - 1];
UpdateTextureID();
}

Expand All @@ -558,7 +555,7 @@ void ImDrawList::PrimReserve(int idx_count, int vtx_count)
IM_ASSERT_PARANOID(idx_count >= 0 && vtx_count >= 0);
if (sizeof(ImDrawIdx) == 2 && (_VtxCurrentIdx + vtx_count >= (1 << 16)) && (Flags & ImDrawListFlags_AllowVtxOffset))
{
_VtxCurrentOffset = VtxBuffer.Size;
_CmdHeader.VtxOffset = VtxBuffer.Size;
_VtxCurrentIdx = 0;
AddDrawCmd();
}
Expand Down Expand Up @@ -1235,9 +1232,9 @@ void ImDrawList::AddText(const ImFont* font, float font_size, const ImVec2& pos,
if (font_size == 0.0f)
font_size = _Data->FontSize;

IM_ASSERT(font->ContainerAtlas->TexID == _TextureIdStack.back()); // Use high-level ImGui::PushFont() or low-level ImDrawList::PushTextureId() to change font.
IM_ASSERT(font->ContainerAtlas->TexID == _CmdHeader.TextureId); // Use high-level ImGui::PushFont() or low-level ImDrawList::PushTextureId() to change font.

ImVec4 clip_rect = _ClipRectStack.back();
ImVec4 clip_rect = _CmdHeader.ClipRect;
if (cpu_fine_clip_rect)
{
clip_rect.x = ImMax(clip_rect.x, cpu_fine_clip_rect->x);
Expand All @@ -1258,7 +1255,7 @@ void ImDrawList::AddImage(ImTextureID user_texture_id, const ImVec2& p_min, cons
if ((col & IM_COL32_A_MASK) == 0)
return;

const bool push_texture_id = _TextureIdStack.empty() || user_texture_id != _TextureIdStack.back();
const bool push_texture_id = user_texture_id != _CmdHeader.TextureId;
if (push_texture_id)
PushTextureID(user_texture_id);

Expand All @@ -1274,7 +1271,7 @@ void ImDrawList::AddImageQuad(ImTextureID user_texture_id, const ImVec2& p1, con
if ((col & IM_COL32_A_MASK) == 0)
return;

const bool push_texture_id = _TextureIdStack.empty() || user_texture_id != _TextureIdStack.back();
const bool push_texture_id = user_texture_id != _CmdHeader.TextureId;
if (push_texture_id)
PushTextureID(user_texture_id);

Expand Down Expand Up @@ -1357,19 +1354,12 @@ void ImDrawListSplitter::Split(ImDrawList* draw_list, int channels_count)
if (_Channels[i]._CmdBuffer.Size == 0)
{
ImDrawCmd draw_cmd;
draw_cmd.ClipRect = draw_list->_ClipRectStack.back();
draw_cmd.TextureId = draw_list->_TextureIdStack.back();
draw_cmd.VtxOffset = draw_list->_VtxCurrentOffset;
ImDrawCmd_HeaderCopy(&draw_cmd, &draw_list->_CmdHeader); // Copy ClipRect, TextureId, VtxOffset
_Channels[i]._CmdBuffer.push_back(draw_cmd);
}
}
}

static inline bool CanMergeDrawCommands(ImDrawCmd* a, ImDrawCmd* b)
{
return memcmp(&a->ClipRect, &b->ClipRect, sizeof(a->ClipRect)) == 0 && a->TextureId == b->TextureId && a->VtxOffset == b->VtxOffset && !a->UserCallback && !b->UserCallback;
}

void ImDrawListSplitter::Merge(ImDrawList* draw_list)
{
// Note that we never use or rely on channels.Size because it is merely a buffer that we never shrink back to 0 to keep all sub-buffers ready for use.
Expand All @@ -1390,12 +1380,16 @@ void ImDrawListSplitter::Merge(ImDrawList* draw_list)
ImDrawChannel& ch = _Channels[i];
if (ch._CmdBuffer.Size > 0 && ch._CmdBuffer.back().ElemCount == 0)
ch._CmdBuffer.pop_back();
if (ch._CmdBuffer.Size > 0 && last_cmd != NULL && CanMergeDrawCommands(last_cmd, &ch._CmdBuffer[0]))
if (ch._CmdBuffer.Size > 0 && last_cmd != NULL)
{
// Merge previous channel last draw command with current channel first draw command if matching.
last_cmd->ElemCount += ch._CmdBuffer[0].ElemCount;
idx_offset += ch._CmdBuffer[0].ElemCount;
ch._CmdBuffer.erase(ch._CmdBuffer.Data); // FIXME-OPT: Improve for multiple merges.
ImDrawCmd* next_cmd = &ch._CmdBuffer[0];
if (ImDrawCmd_HeaderCompare(last_cmd, next_cmd) == 0 && last_cmd->UserCallback == NULL && next_cmd->UserCallback == NULL)
{
// Merge previous channel last draw command with current channel first draw command if matching.
last_cmd->ElemCount += next_cmd->ElemCount;
idx_offset += next_cmd->ElemCount;
ch._CmdBuffer.erase(ch._CmdBuffer.Data); // FIXME-OPT: Improve for multiple merges.
}
}
if (ch._CmdBuffer.Size > 0)
last_cmd = &ch._CmdBuffer.back();
Expand Down

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