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Fix for draw list splitter generating incorrect vertex offsets when v…
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…ertex count exceeds index size (ocornut#3129)
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@ShironekoBen @thedmd
ShironekoBen authored and thedmd committed Jun 4, 2020
1 parent 79fbab5 commit 0d94847
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Showing 2 changed files with 85 additions and 2 deletions.
73 changes: 73 additions & 0 deletions examples/example_win32_directx11/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,75 @@ void CreateRenderTarget();
void CleanupRenderTarget();
LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

#include <random>
void ShowBackendCheckerWindow(bool* p_open)
{
if (!ImGui::Begin("Dear ImGui Backend Checker", p_open))
{
ImGui::End();
return;
}

ImGuiIO& io = ImGui::GetIO();
ImGui::Text("Dear ImGui %s Backend Checker", ImGui::GetVersion());
ImGui::Text("io.BackendPlatformName: %s", io.BackendPlatformName ? io.BackendPlatformName : "NULL");
ImGui::Text("io.BackendRendererName: %s", io.BackendRendererName ? io.BackendRendererName : "NULL");
ImGui::Text("RendererHasVtxOffset: %s", ((io.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset) != 0) ? "True" : "False");
ImGui::Text("sizeof(ImDrawIdx): %d", sizeof(ImDrawIdx));
ImGui::Separator();

//if (ImGui::TreeNode("0001: Renderer: Large Mesh Support"))
{
ImDrawList* draw_list = ImGui::GetWindowDrawList();
{
static int vtx_count = 64722;// 60000;
ImGui::SliderInt("VtxCount##1", &vtx_count, 0, 100000);

static int map[100000 / 4];
for (int n = 0; n < vtx_count / 4; n++)
map[n] = n;
std::srand(13);
std::random_shuffle(std::begin(map), std::end(map), [](auto n) { return std::rand() % n; });

ImDrawListSplitter splitter;
splitter.Split(draw_list, 100000 / 4);

ImVec2 p = ImGui::GetCursorScreenPos();
for (int n = 0; n < vtx_count / 4; n++)
{
splitter.SetCurrentChannel(draw_list, map[n]);

float off_x = (float)(n % 100) * 3.0f;
float off_y = (float)(n % 100) * 1.0f;
ImU32 col = IM_COL32(((n * 17) & 255), ((n * 59) & 255), ((n * 83) & 255), 255);
draw_list->AddRectFilled(ImVec2(p.x + off_x, p.y + off_y), ImVec2(p.x + off_x + 50, p.y + off_y + 50), col);
}

splitter.Merge(draw_list);

ImGui::Dummy(ImVec2(300 + 50, 100 + 50));
ImGui::Text("VtxBuffer.Size = %d", draw_list->VtxBuffer.Size);
}
{
static int vtx_count = 60000;
ImGui::SliderInt("VtxCount##2", &vtx_count, 0, 100000);
ImVec2 p = ImGui::GetCursorScreenPos();
for (int n = 0; n < vtx_count / (10 * 4); n++)
{
float off_x = (float)(n % 100) * 3.0f;
float off_y = (float)(n % 100) * 1.0f;
ImU32 col = IM_COL32(((n * 17) & 255), ((n * 59) & 255), ((n * 83) & 255), 255);
draw_list->AddText(ImVec2(p.x + off_x, p.y + off_y), col, "ABCDEFGHIJ");
}
ImGui::Dummy(ImVec2(300 + 50, 100 + 20));
ImGui::Text("VtxBuffer.Size = %d", draw_list->VtxBuffer.Size);
}
//ImGui::TreePop();
}

ImGui::End();
}

// Main code
int main(int, char**)
{
Expand Down Expand Up @@ -99,6 +168,10 @@ int main(int, char**)
ImGui_ImplWin32_NewFrame();
ImGui::NewFrame();

static bool show_check_window = true;
if (show_check_window)
ShowBackendCheckerWindow(&show_check_window);

// 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
if (show_demo_window)
ImGui::ShowDemoWindow(&show_demo_window);
Expand Down
14 changes: 12 additions & 2 deletions imgui_draw.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -461,7 +461,7 @@ void ImDrawList::UpdateClipRect()

// Try to merge with previous command if it matches, else use current command
ImDrawCmd* prev_cmd = CmdBuffer.Size > 1 ? curr_cmd - 1 : NULL;
if (curr_cmd->ElemCount == 0 && prev_cmd && memcmp(&prev_cmd->ClipRect, &curr_clip_rect, sizeof(ImVec4)) == 0 && prev_cmd->TextureId == GetCurrentTextureId() && prev_cmd->UserCallback == NULL)
if (curr_cmd->ElemCount == 0 && prev_cmd && 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();
else
curr_cmd->ClipRect = curr_clip_rect;
Expand All @@ -480,7 +480,7 @@ void ImDrawList::UpdateTextureID()

// Try to merge with previous command if it matches, else use current command
ImDrawCmd* prev_cmd = CmdBuffer.Size > 1 ? curr_cmd - 1 : NULL;
if (curr_cmd->ElemCount == 0 && prev_cmd && prev_cmd->TextureId == curr_texture_id && memcmp(&prev_cmd->ClipRect, &GetCurrentClipRect(), sizeof(ImVec4)) == 0 && prev_cmd->UserCallback == NULL)
if (curr_cmd->ElemCount == 0 && prev_cmd && 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();
else
curr_cmd->TextureId = curr_texture_id;
Expand Down Expand Up @@ -1403,6 +1403,8 @@ void ImDrawListSplitter::Merge(ImDrawList* draw_list)
if (int sz = ch._IdxBuffer.Size) { memcpy(idx_write, ch._IdxBuffer.Data, sz * sizeof(ImDrawIdx)); idx_write += sz; }
}
draw_list->_IdxWritePtr = idx_write;
if ((draw_list->CmdBuffer.Size > 0) && (draw_list->CmdBuffer.Data[draw_list->CmdBuffer.Size - 1].VtxOffset != draw_list->_VtxCurrentOffset))
draw_list->AddDrawCmd(); // If the vertex offset has changed we need a new draw command
draw_list->UpdateClipRect(); // We call this instead of AddDrawCmd(), so that empty channels won't produce an extra draw call.
draw_list->UpdateTextureID();
_Count = 1;
Expand All @@ -1413,13 +1415,21 @@ void ImDrawListSplitter::SetCurrentChannel(ImDrawList* draw_list, int idx)
IM_ASSERT(idx >= 0 && idx < _Count);
if (_Current == idx)
return;
ImDrawCmd* old_curr_cmd = (draw_list->CmdBuffer.Size > 0) ? &draw_list->CmdBuffer.Data[draw_list->CmdBuffer.Size - 1] : NULL; // The "old" current command
// Overwrite ImVector (12/16 bytes), four times. This is merely a silly optimization instead of doing .swap()
memcpy(&_Channels.Data[_Current]._CmdBuffer, &draw_list->CmdBuffer, sizeof(draw_list->CmdBuffer));
memcpy(&_Channels.Data[_Current]._IdxBuffer, &draw_list->IdxBuffer, sizeof(draw_list->IdxBuffer));
_Current = idx;
memcpy(&draw_list->CmdBuffer, &_Channels.Data[idx]._CmdBuffer, sizeof(draw_list->CmdBuffer));
memcpy(&draw_list->IdxBuffer, &_Channels.Data[idx]._IdxBuffer, sizeof(draw_list->IdxBuffer));
draw_list->_IdxWritePtr = draw_list->IdxBuffer.Data + draw_list->IdxBuffer.Size;
// If the vertex offset or clip rect changed then we need a new draw call (FIXME: What about user callbacks?)
if (draw_list->CmdBuffer.Size > 0)
{
ImDrawCmd* new_curr_cmd = &draw_list->CmdBuffer.Data[draw_list->CmdBuffer.Size - 1]; // The "new" current command
if ((new_curr_cmd->VtxOffset != draw_list->_VtxCurrentOffset) || (old_curr_cmd && (memcmp(&new_curr_cmd->ClipRect, &old_curr_cmd->ClipRect, sizeof(ImVec4)) != 0)))
draw_list->AddDrawCmd();
}
}

//-----------------------------------------------------------------------------
Expand Down

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