TextAlignedV(): better handling of cursor position and DC boundary

[dkosmari]

The current TextAlignedV() leaves the position and boundary in an inconsistent state, that limits its usefulness.

With this PR:

• The widget always has width width (parameter was called size_x before), unless:
  • width == 0 means the real text width, as obtained by CalcTextSize().x. Before, size_x == 0 was giving me no rendered output, as if it was actually clipping the text to a zero-width region.
  • width < 0 means ContentRegionAvail().x.
• Cursor position actually matches the right of the displayed text.
• DC boundary is updated according to the actual displayed text.

Here's a test code (call test_text_aligned() from any example code), showing the bounding box, cursor position behavior, and how it behaves inside table cells:

void show_bounding_box()
{
    ImVec2 min = ImGui::GetItemRectMin();
    ImVec2 max = ImGui::GetItemRectMax();
    ImU32 col = ImGui::GetColorU32(ImVec4{1.0f, 0.0f, 0.0f, 0.5f});
    ImDrawList* draw_list = ImGui::GetCurrentWindow()->DrawList;
    draw_list->AddRect(min, max, col);
}

void test_text_aligned()
{
    static float width = 200.0f;
    static float align = 0.0f;
    if (ImGui::Begin("Test TextAligned()")) {

        ImGui::TextWrapped("Test cursor positioning and bounding box.");

        ImVec2 available = ImGui::GetContentRegionAvail();
        ImGui::SliderFloat("align", &align, 0.0f, 1.0f);
        ImGui::DragFloat("width", &width, 1.0f, -1.0f, available.x, "%.0f");
        ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, {0, 0});
        if (ImGui::BeginChild("container", {},
                              ImGuiChildFlags_Borders | ImGuiChildFlags_AutoResizeY,
                              ImGuiWindowFlags_HorizontalScrollbar)) {
            ImGui::AlignTextToFramePadding();
            ImGui::TextAligned(align, width, "Irish wristwatch");
            show_bounding_box();
            ImGui::SameLine();
            ImGui::Button("##test", {10, 0});

            ImGui::Button("##test2", {10, 0});
            ImGui::SameLine();
            ImGui::TextAligned(align, width, "Rear wheel drive");
            show_bounding_box();
        }
        ImGui::EndChild();
        ImGui::PopStyleVar();

        ImGui::Separator();

        ImGui::TextWrapped("Test inside a table.");

        if (ImGui::BeginTable("table", 3,
                              ImGuiTableFlags_Borders |
                              ImGuiTableFlags_Resizable)) {

            static float apple_align  = 0.0f;
            static float banana_align = 0.5f;
            static float cherry_align = 1.0f;

            ImGui::TableNextRow(ImGuiTableRowFlags_Headers);
            ImGui::TableNextColumn();
            ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
            ImGui::SliderFloat("##apple_align", &apple_align, 0.0f, 1.0f);
            ImGui::TableNextColumn();
            ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
            ImGui::SliderFloat("##banana_align", &banana_align, 0.0f, 1.0f);
            ImGui::TableNextColumn();
            ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
            ImGui::SliderFloat("##cherry_align", &cherry_align, 0.0f, 1.0f);

            ImGui::TableNextRow();
            ImGui::TableNextColumn();
            ImGui::TextAligned(apple_align, -1.0f, "Apple");
            ImGui::TableNextColumn();
            ImGui::TextAligned(banana_align, -1.0f, "Banana");
            ImGui::TableNextColumn();
            ImGui::TextAligned(cherry_align, -1.0f, "Cherry");

            ImGui::EndTable();
        }
    }
    ImGui::End();
}

Here are images showing different outputs: