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Add offset and stride to ImPlotGetter plots #609

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3dea4f2
Add offset and stride to ImPlotGetter plots
GameChaos Feb 15, 2025
ed34e67
Add idx_ prefix to offset, stride and add downsample demo
GameChaos Jan 3, 2026
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12 changes: 6 additions & 6 deletions implot.h
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Original file line number Diff line number Diff line change
Expand Up @@ -857,28 +857,28 @@ IMPLOT_API void SetNextAxesToFit();
// Plots a standard 2D line plot.
IMPLOT_TMP void PlotLine(const char* label_id, const T* values, int count, double xscale=1, double xstart=0, ImPlotLineFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotLine(const char* label_id, const T* xs, const T* ys, int count, ImPlotLineFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotLineG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotLineFlags flags=0);
IMPLOT_API void PlotLineG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotLineFlags flags=0, int offset=0, int stride=1); // offset and stride aren't in bytes, they act on the index, ie: idx * offset + stride
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// Plots a standard 2D scatter plot. Default marker is ImPlotMarker_Circle.
IMPLOT_TMP void PlotScatter(const char* label_id, const T* values, int count, double xscale=1, double xstart=0, ImPlotScatterFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotScatter(const char* label_id, const T* xs, const T* ys, int count, ImPlotScatterFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotScatterG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotScatterFlags flags=0);
IMPLOT_API void PlotScatterG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotScatterFlags flags=0, int offset=0, int stride=1);

// Plots a a stairstep graph. The y value is continued constantly to the right from every x position, i.e. the interval [x[i], x[i+1]) has the value y[i]
IMPLOT_TMP void PlotStairs(const char* label_id, const T* values, int count, double xscale=1, double xstart=0, ImPlotStairsFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotStairs(const char* label_id, const T* xs, const T* ys, int count, ImPlotStairsFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotStairsG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotStairsFlags flags=0);
IMPLOT_API void PlotStairsG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotStairsFlags flags=0, int offset=0, int stride=1);

// Plots a shaded (filled) region between two lines, or a line and a horizontal reference. Set yref to +/-INFINITY for infinite fill extents.
IMPLOT_TMP void PlotShaded(const char* label_id, const T* values, int count, double yref=0, double xscale=1, double xstart=0, ImPlotShadedFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotShaded(const char* label_id, const T* xs, const T* ys, int count, double yref=0, ImPlotShadedFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotShaded(const char* label_id, const T* xs, const T* ys1, const T* ys2, int count, ImPlotShadedFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotShadedG(const char* label_id, ImPlotGetter getter1, void* data1, ImPlotGetter getter2, void* data2, int count, ImPlotShadedFlags flags=0);
IMPLOT_API void PlotShadedG(const char* label_id, ImPlotGetter getter1, void* data1, ImPlotGetter getter2, void* data2, int count, ImPlotShadedFlags flags=0, int offset=0, int stride=1);

// Plots a bar graph. Vertical by default. #bar_size and #shift are in plot units.
IMPLOT_TMP void PlotBars(const char* label_id, const T* values, int count, double bar_size=0.67, double shift=0, ImPlotBarsFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_TMP void PlotBars(const char* label_id, const T* xs, const T* ys, int count, double bar_size, ImPlotBarsFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotBarsG(const char* label_id, ImPlotGetter getter, void* data, int count, double bar_size, ImPlotBarsFlags flags=0);
IMPLOT_API void PlotBarsG(const char* label_id, ImPlotGetter getter, void* data, int count, double bar_size, ImPlotBarsFlags flags=0, int offset=0, int stride=1);

// Plots a group of bars. #values is a row-major matrix with #item_count rows and #group_count cols. #label_ids should have #item_count elements.
IMPLOT_TMP void PlotBarGroups(const char* const label_ids[], const T* values, int item_count, int group_count, double group_size=0.67, double shift=0, ImPlotBarGroupsFlags flags=0);
Expand Down Expand Up @@ -911,7 +911,7 @@ IMPLOT_TMP double PlotHistogram2D(const char* label_id, const T* xs, const T* ys

// Plots digital data. Digital plots do not respond to y drag or zoom, and are always referenced to the bottom of the plot.
IMPLOT_TMP void PlotDigital(const char* label_id, const T* xs, const T* ys, int count, ImPlotDigitalFlags flags=0, int offset=0, int stride=sizeof(T));
IMPLOT_API void PlotDigitalG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotDigitalFlags flags=0);
IMPLOT_API void PlotDigitalG(const char* label_id, ImPlotGetter getter, void* data, int count, ImPlotDigitalFlags flags=0, int offset=0, int stride=1);

// Plots an axis-aligned image. #bounds_min/bounds_max are in plot coordinates (y-up) and #uv0/uv1 are in texture coordinates (y-down).
IMPLOT_API void PlotImage(const char* label_id, ImTextureID user_texture_id, const ImPlotPoint& bounds_min, const ImPlotPoint& bounds_max, const ImVec2& uv0=ImVec2(0,0), const ImVec2& uv1=ImVec2(1,1), const ImVec4& tint_col=ImVec4(1,1,1,1), ImPlotImageFlags flags=0);
Expand Down
38 changes: 21 additions & 17 deletions implot_items.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -571,17 +571,21 @@ struct GetterXY {

/// Interprets a user's function pointer as ImPlotPoints
struct GetterFuncPtr {
GetterFuncPtr(ImPlotGetter getter, void* data, int count) :
GetterFuncPtr(ImPlotGetter getter, void* data, int count, int offset, int stride) :
Getter(getter),
Data(data),
Count(count)
Count(count),
Offset(offset),
Stride(stride)
{ }
template <typename I> IMPLOT_INLINE ImPlotPoint operator()(I idx) const {
return Getter(idx, Data);
return Getter(idx * Stride + Offset, Data);

@brenocq brenocq Dec 21, 2025

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To be consistent with the byte-wise offset/stride, it would be better to do something like (idx * Stride + Offset) % Count.

@GameChaos GameChaos Jan 3, 2026 •
edited
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this breaks downsampling though, because idx is often much higher than count due to offset. i'd even say it's a bug in the byte-wise offset / stride code that makes implementing downsampling impossible there because the data starts looping itself when zooming in. makes sense why my downsampling code broke at some point with the non-getter functions haha.

}
ImPlotGetter Getter;
void* const Data;
const int Count;
const int Offset;
const int Stride;
};

template <typename _Getter>
Expand Down Expand Up @@ -1635,8 +1639,8 @@ CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

// custom
void PlotLineG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotLineFlags flags) {
GetterFuncPtr getter(getter_func,data, count);
void PlotLineG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotLineFlags flags, int offset, int stride) {
GetterFuncPtr getter(getter_func,data, count, offset, stride);
PlotLineEx(label_id, getter, flags);
}

Expand Down Expand Up @@ -1685,8 +1689,8 @@ CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

// custom
void PlotScatterG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotScatterFlags flags) {
GetterFuncPtr getter(getter_func,data, count);
void PlotScatterG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotScatterFlags flags, int offset, int stride) {
GetterFuncPtr getter(getter_func,data, count, offset, stride);
return PlotScatterEx(label_id, getter, flags);
}

Expand Down Expand Up @@ -1749,8 +1753,8 @@ CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

// custom
void PlotStairsG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotStairsFlags flags) {
GetterFuncPtr getter(getter_func,data, count);
void PlotStairsG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotStairsFlags flags, int offset, int stride) {
GetterFuncPtr getter(getter_func,data, count, offset, stride);
return PlotStairsEx(label_id, getter, flags);
}

Expand Down Expand Up @@ -1812,9 +1816,9 @@ CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

// custom
void PlotShadedG(const char* label_id, ImPlotGetter getter_func1, void* data1, ImPlotGetter getter_func2, void* data2, int count, ImPlotShadedFlags flags) {
GetterFuncPtr getter1(getter_func1, data1, count);
GetterFuncPtr getter2(getter_func2, data2, count);
void PlotShadedG(const char* label_id, ImPlotGetter getter_func1, void* data1, ImPlotGetter getter_func2, void* data2, int count, ImPlotShadedFlags flags, int offset, int stride) {
GetterFuncPtr getter1(getter_func1, data1, count, offset, stride);
GetterFuncPtr getter2(getter_func2, data2, count, offset, stride);
PlotShadedEx(label_id, getter1, getter2, flags);
}

Expand Down Expand Up @@ -1904,14 +1908,14 @@ void PlotBars(const char* label_id, const T* xs, const T* ys, int count, double
CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

void PlotBarsG(const char* label_id, ImPlotGetter getter_func, void* data, int count, double bar_size, ImPlotBarsFlags flags) {
void PlotBarsG(const char* label_id, ImPlotGetter getter_func, void* data, int count, double bar_size, ImPlotBarsFlags flags, int offset, int stride) {
if (ImHasFlag(flags, ImPlotBarsFlags_Horizontal)) {
GetterFuncPtr getter1(getter_func, data, count);
GetterFuncPtr getter1(getter_func, data, count, offset, stride);
GetterOverrideX<GetterFuncPtr> getter2(getter1,0);
PlotBarsHEx(label_id, getter1, getter2, bar_size, flags);
}
else {
GetterFuncPtr getter1(getter_func, data, count);
GetterFuncPtr getter1(getter_func, data, count, offset, stride);
GetterOverrideY<GetterFuncPtr> getter2(getter1,0);
PlotBarsVEx(label_id, getter1, getter2, bar_size, flags);
}
Expand Down Expand Up @@ -2779,8 +2783,8 @@ CALL_INSTANTIATE_FOR_NUMERIC_TYPES()
#undef INSTANTIATE_MACRO

// custom
void PlotDigitalG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotDigitalFlags flags) {
GetterFuncPtr getter(getter_func,data,count);
void PlotDigitalG(const char* label_id, ImPlotGetter getter_func, void* data, int count, ImPlotDigitalFlags flags, int offset, int stride) {
GetterFuncPtr getter(getter_func,data,count, offset, stride);
return PlotDigitalEx(label_id, getter, flags);
}

Expand Down