SetScrollX/SetScrollY is not symmetrical #6677

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opened 2023-08-02 12:36:02 +00:00 by tombuskens · 0 comments

tombuskens commented

2023-08-02 12:36:02 +00:00

(Migrated from github.com)

Version/Branch of Dear ImGui:

Dear ImGui 1.89.7 WIP (18962)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=202002
define: _WIN32
define: _WIN64
define: _MSC_VER=1936
define: _MSVC_LANG=202002
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_win32
io.BackendRendererName: imgui_impl_dx12
io.ConfigFlags: 0x00000441
 NavEnableKeyboard
 DockingEnable
 ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1264.00,761.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 0.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00

My Issue/Question:

Observed behavior
When using either SetScrollX or SetScrollY to scroll small increments, scrolling the same amount in a different direction (e.g.

float x_offset = scrollLeft ? -0.8f : 0.8f; 
ImGui::SetScrollX(ImGui::GetScrollX() + x_offset );

will result in either

content will scroll in one direction, but not the other - when abs(x_offset) is smaller than 1.0f
content will scroll noticeably faster in one direction, when abs(x_offset) is small, but larger than 1.0f

Expected behavior
The expected behavior would be to scroll the same amount in both directions.

Potential fix
It looks like this is caused by the IM_FLOOR call in CalcNextScrollFromScrollTargetAndClamp. Replacing IM_FLOOR with IM_ROUND seems to solve the issue.

Standalone, minimal, complete and verifiable example:
Code modified from the Layout/Scrolling/Horizontal (more) demo. Only change is fixing scroll_x_delta to +/-0.8f.

        static int lines = 7;
        ImGui::PushStyleVar(ImGuiStyleVar_FrameRounding, 3.0f);
        ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(2.0f, 1.0f));
        ImVec2 scrolling_child_size = ImVec2(0, ImGui::GetFrameHeightWithSpacing() * 7 + 30);
        ImGui::BeginChild("scrolling", scrolling_child_size, true, ImGuiWindowFlags_HorizontalScrollbar);
        for (int line = 0; line < lines; line++)
        {
            // Display random stuff. For the sake of this trivial demo we are using basic Button() + SameLine()
            // If you want to create your own time line for a real application you may be better off manipulating
            // the cursor position yourself, aka using SetCursorPos/SetCursorScreenPos to position the widgets
            // yourself. You may also want to use the lower-level ImDrawList API.
            int num_buttons = 10 + ((line & 1) ? line * 9 : line * 3);
            for (int n = 0; n < num_buttons; n++)
            {
                if (n > 0) ImGui::SameLine();
                ImGui::PushID(n + line * 1000);
                char num_buf[16];
                sprintf(num_buf, "%d", n);
                const char* label = (!(n % 15)) ? "FizzBuzz" : (!(n % 3)) ? "Fizz" : (!(n % 5)) ? "Buzz" : num_buf;
                float hue = n * 0.05f;
                ImGui::PushStyleColor(ImGuiCol_Button, (ImVec4)ImColor::HSV(hue, 0.6f, 0.6f));
                ImGui::PushStyleColor(ImGuiCol_ButtonHovered, (ImVec4)ImColor::HSV(hue, 0.7f, 0.7f));
                ImGui::PushStyleColor(ImGuiCol_ButtonActive, (ImVec4)ImColor::HSV(hue, 0.8f, 0.8f));
                ImGui::Button(label, ImVec2(40.0f + sinf((float)(line + n)) * 20.0f, 0.0f));
                ImGui::PopStyleColor(3);
                ImGui::PopID();
            }
        }
        float scroll_x = ImGui::GetScrollX();
        float scroll_max_x = ImGui::GetScrollMaxX();
        ImGui::EndChild();
        ImGui::PopStyleVar(2);
        float scroll_x_delta = 0.0f;
        ImGui::SmallButton("<<");
        if (ImGui::IsItemActive())
            scroll_x_delta = -0.8f; // <== CHANGED: use a small fixed small increment
        ImGui::SameLine();
        ImGui::Text("Scroll from code"); ImGui::SameLine();
        ImGui::SmallButton(">>");
        if (ImGui::IsItemActive())
            scroll_x_delta = +0.8f;  // <== CHANGED: use a small fixed small increment
        ImGui::SameLine();
        ImGui::Text("%.0f/%.0f", scroll_x, scroll_max_x);
        if (scroll_x_delta != 0.0f)
        {
            // Demonstrate a trick: you can use Begin to set yourself in the context of another window
            // (here we are already out of your child window)
            ImGui::BeginChild("scrolling");
            ImGui::SetScrollX(ImGui::GetScrollX() + scroll_x_delta);
            ImGui::EndChild();
        }

**Version/Branch of Dear ImGui:** ``` Dear ImGui 1.89.7 WIP (18962) -------------------------------- sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20 define: __cplusplus=202002 define: _WIN32 define: _WIN64 define: _MSC_VER=1936 define: _MSVC_LANG=202002 define: IMGUI_HAS_VIEWPORT define: IMGUI_HAS_DOCK -------------------------------- io.BackendPlatformName: imgui_impl_win32 io.BackendRendererName: imgui_impl_dx12 io.ConfigFlags: 0x00000441 NavEnableKeyboard DockingEnable ViewportsEnable io.ConfigViewportsNoDecoration io.ConfigInputTextCursorBlink io.ConfigWindowsResizeFromEdges io.ConfigMemoryCompactTimer = 60.0 io.BackendFlags: 0x00001C0E HasMouseCursors HasSetMousePos PlatformHasViewports HasMouseHoveredViewport RendererHasVtxOffset RendererHasViewports -------------------------------- io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64 io.DisplaySize: 1264.00,761.00 io.DisplayFramebufferScale: 1.00,1.00 -------------------------------- style.WindowPadding: 8.00,8.00 style.WindowBorderSize: 1.00 style.FramePadding: 4.00,3.00 style.FrameRounding: 0.00 style.FrameBorderSize: 0.00 style.ItemSpacing: 8.00,4.00 style.ItemInnerSpacing: 4.00,4.00 ``` **My Issue/Question:** ***Observed behavior*** When using either `SetScrollX` or `SetScrollY` to scroll small increments, scrolling the same amount in a different direction (e.g. ``` float x_offset = scrollLeft ? -0.8f : 0.8f; ImGui::SetScrollX(ImGui::GetScrollX() + x_offset ); ``` will result in either - content will scroll in one direction, but not the other - when abs(x_offset) is smaller than 1.0f - content will scroll noticeably faster in one direction, when abs(x_offset) is small, but larger than 1.0f ***Expected behavior*** The expected behavior would be to scroll the same amount in both directions. ***Potential fix*** It looks like this is caused by the `IM_FLOOR` call in `CalcNextScrollFromScrollTargetAndClamp`. Replacing `IM_FLOOR` with `IM_ROUND` seems to solve the issue. **Standalone, minimal, complete and verifiable example:** Code modified from the _Layout/Scrolling/Horizontal (more)_ demo. Only change is fixing `scroll_x_delta` to `+/-0.8f`. ``` static int lines = 7; ImGui::PushStyleVar(ImGuiStyleVar_FrameRounding, 3.0f); ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(2.0f, 1.0f)); ImVec2 scrolling_child_size = ImVec2(0, ImGui::GetFrameHeightWithSpacing() * 7 + 30); ImGui::BeginChild("scrolling", scrolling_child_size, true, ImGuiWindowFlags_HorizontalScrollbar); for (int line = 0; line < lines; line++) { // Display random stuff. For the sake of this trivial demo we are using basic Button() + SameLine() // If you want to create your own time line for a real application you may be better off manipulating // the cursor position yourself, aka using SetCursorPos/SetCursorScreenPos to position the widgets // yourself. You may also want to use the lower-level ImDrawList API. int num_buttons = 10 + ((line & 1) ? line * 9 : line * 3); for (int n = 0; n < num_buttons; n++) { if (n > 0) ImGui::SameLine(); ImGui::PushID(n + line * 1000); char num_buf[16]; sprintf(num_buf, "%d", n); const char* label = (!(n % 15)) ? "FizzBuzz" : (!(n % 3)) ? "Fizz" : (!(n % 5)) ? "Buzz" : num_buf; float hue = n * 0.05f; ImGui::PushStyleColor(ImGuiCol_Button, (ImVec4)ImColor::HSV(hue, 0.6f, 0.6f)); ImGui::PushStyleColor(ImGuiCol_ButtonHovered, (ImVec4)ImColor::HSV(hue, 0.7f, 0.7f)); ImGui::PushStyleColor(ImGuiCol_ButtonActive, (ImVec4)ImColor::HSV(hue, 0.8f, 0.8f)); ImGui::Button(label, ImVec2(40.0f + sinf((float)(line + n)) * 20.0f, 0.0f)); ImGui::PopStyleColor(3); ImGui::PopID(); } } float scroll_x = ImGui::GetScrollX(); float scroll_max_x = ImGui::GetScrollMaxX(); ImGui::EndChild(); ImGui::PopStyleVar(2); float scroll_x_delta = 0.0f; ImGui::SmallButton("<<"); if (ImGui::IsItemActive()) scroll_x_delta = -0.8f; // <== CHANGED: use a small fixed small increment ImGui::SameLine(); ImGui::Text("Scroll from code"); ImGui::SameLine(); ImGui::SmallButton(">>"); if (ImGui::IsItemActive()) scroll_x_delta = +0.8f; // <== CHANGED: use a small fixed small increment ImGui::SameLine(); ImGui::Text("%.0f/%.0f", scroll_x, scroll_max_x); if (scroll_x_delta != 0.0f) { // Demonstrate a trick: you can use Begin to set yourself in the context of another window // (here we are already out of your child window) ImGui::BeginChild("scrolling"); ImGui::SetScrollX(ImGui::GetScrollX() + scroll_x_delta); ImGui::EndChild(); } ```