Add perspective support (rect to rect) to Viewer

Change-Id: I312d5b3e6b7f37a3a7bfd5561bcdb31b43e207b8
Reviewed-on: https://skia-review.googlesource.com/123934
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>

2 files changed, 88 insertions, 2 deletions

diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 04426ffc7e..3411e5684b 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -178,6 +178,7 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
     , fZoomLevel(0.0f)
     , fRotation(0.0f)
     , fGestureDevice(GestureDevice::kNone)
+    , fPerspective(false)
     , fTileCnt(0)
     , fThreadCnt(0)
 {
@@ -494,6 +495,10 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
         this->listNames();
     }
 
+    fPerspectivePoints[0].set(0, 0);
+    fPerspectivePoints[1].set(1, 0);
+    fPerspectivePoints[2].set(0, 1);
+    fPerspectivePoints[3].set(1, 1);
     fAnimTimer.run();
 
     auto gamutImage = GetResourceAsImage("images/gamut.png");
@@ -878,6 +883,21 @@ SkMatrix Viewer::computePreTouchMatrix() {
                                           : SK_Scalar1 + fZoomLevel;
     m.preScale(zoomScale, zoomScale);
     m.preRotate(fRotation);
+
+    if (fPerspective) {
+        SkScalar w = fWindow->width(), h = fWindow->height();
+        SkPoint orthoPts[4] = { { 0, 0 }, { w, 0 }, { 0, h }, { w, h } };
+        SkPoint perspPts[4] = {
+            { fPerspectivePoints[0].fX * w, fPerspectivePoints[0].fY * h },
+            { fPerspectivePoints[1].fX * w, fPerspectivePoints[1].fY * h },
+            { fPerspectivePoints[2].fX * w, fPerspectivePoints[2].fY * h },
+            { fPerspectivePoints[3].fX * w, fPerspectivePoints[3].fY * h }
+        };
+        SkMatrix persp;
+        persp.setPolyToPoly(orthoPts, perspPts, 4);
+        m.preConcat(persp);
+    }
+
     return m;
 }
 
@@ -1204,7 +1224,6 @@ static void ImGui_Primaries(SkColorSpacePrimaries* primaries, SkPaint* gamutPain
     // Magic numbers are pixel locations of the origin and upper-right corner.
     drawList->AddImage(gamutPaint, pos, ImVec2(pos.x + size.x, pos.y + size.y),
                        ImVec2(242, 61), ImVec2(1897, 1922));
-    ImVec2 endPos = ImGui::GetCursorPos();
 
     // Primary markers
     ImVec2 r = ImGui_DragPrimary("R", &primaries->fRX, &primaries->fRY, pos, size);
@@ -1220,7 +1239,65 @@ static void ImGui_Primaries(SkColorSpacePrimaries* primaries, SkPaint* gamutPain
     drawList->AddTriangle(r, g, b, 0xFFFFFFFF);
 
     // Re-position cursor immediate after the diagram for subsequent controls
-    ImGui::SetCursorPos(endPos);
+    ImGui::SetCursorScreenPos(ImVec2(pos.x, pos.y + size.y));
+}
+
+static ImVec2 ImGui_DragPoint(const char* label, SkPoint* p,
+                              const ImVec2& pos, const ImVec2& size, bool* dragging) {
+    // Transform points ([0, 0] - [1.0, 1.0]) to screen coords
+    ImVec2 center(pos.x + p->fX * size.x, pos.y + p->fY * size.y);
+
+    // Invisible 10x10 button
+    ImGui::SetCursorScreenPos(ImVec2(center.x - 5, center.y - 5));
+    ImGui::InvisibleButton(label, ImVec2(10, 10));
+
+    if (ImGui::IsItemActive() && ImGui::IsMouseDragging()) {
+        ImGuiIO& io = ImGui::GetIO();
+        // Normalized mouse position, relative to our gamut box
+        ImVec2 mousePosXY((io.MousePos.x - pos.x) / size.x, (io.MousePos.y - pos.y) / size.y);
+        // Clamp to edge of box
+        p->fX = SkTPin(mousePosXY.x, 0.0f, 1.0f);
+        p->fY = SkTPin(mousePosXY.y, 0.0f, 1.0f);
+        *dragging = true;
+    }
+
+    // Return screen coordinates for the caller. We could just return center here, but we'd have
+    // one frame of lag during drag.
+    return ImVec2(pos.x + p->fX * size.x, pos.y + p->fY * size.y);
+}
+
+static bool ImGui_DragQuad(SkPoint* pts) {
+    ImDrawList* drawList = ImGui::GetWindowDrawList();
+
+    // Fit our image/canvas to the available width, and scale the height to maintain aspect ratio.
+    float canvasWidth = SkTMax(ImGui::GetContentRegionAvailWidth(), 50.0f);
+    ImVec2 size = ImVec2(canvasWidth, canvasWidth);
+    ImVec2 pos = ImGui::GetCursorScreenPos();
+
+    // Background rectangle
+    drawList->AddRectFilled(pos, ImVec2(pos.x + size.x, pos.y + size.y), IM_COL32(0, 0, 0, 128));
+
+    // Corner markers
+    bool dragging = false;
+    ImVec2 tl = ImGui_DragPoint("TL", pts + 0, pos, size, &dragging);
+    ImVec2 tr = ImGui_DragPoint("TR", pts + 1, pos, size, &dragging);
+    ImVec2 bl = ImGui_DragPoint("BL", pts + 2, pos, size, &dragging);
+    ImVec2 br = ImGui_DragPoint("BR", pts + 3, pos, size, &dragging);
+
+    // Draw markers and quad
+    drawList->AddCircle(tl, 5.0f, 0xFFFFFFFF);
+    drawList->AddCircle(tr, 5.0f, 0xFFFFFFFF);
+    drawList->AddCircle(bl, 5.0f, 0xFFFFFFFF);
+    drawList->AddCircle(br, 5.0f, 0xFFFFFFFF);
+    drawList->AddLine(tl, tr, 0xFFFFFFFF);
+    drawList->AddLine(tr, br, 0xFFFFFFFF);
+    drawList->AddLine(br, bl, 0xFFFFFFFF);
+    drawList->AddLine(bl, tl, 0xFFFFFFFF);
+
+    ImGui::SetCursorScreenPos(ImVec2(pos.x, pos.y + size.y));
+    ImGui::Spacing();
+
+    return dragging;
 }
 
 void Viewer::drawImGui() {
@@ -1356,6 +1433,12 @@ void Viewer::drawImGui() {
                     this->preTouchMatrixChanged();
                     paramsChanged = true;
                 }
+                if (ImGui::Checkbox("Perspective", &fPerspective)) {
+                    this->preTouchMatrixChanged();
+                }
+                if (ImGui_DragQuad(fPerspectivePoints)) {
+                    this->preTouchMatrixChanged();
+                }
             }
 
             if (ImGui::CollapsingHeader("Paint")) {
diff --git a/tools/viewer/Viewer.h b/tools/viewer/Viewer.h
index 25cbed656c..be35a88525 100644
--- a/tools/viewer/Viewer.h
+++ b/tools/viewer/Viewer.h
@@ -158,6 +158,9 @@ private:
     // identity unless the window initially scales the content to fit the screen.
     SkMatrix               fDefaultMatrix;
 
+    bool                   fPerspective;
+    SkPoint                fPerspectivePoints[4];
+
     SkTArray<std::function<void(void)>> fDeferredActions;
 
     Json::Value            fAllSlideNames; // cache all slide names for fast updateUIState