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Mirror anchor offset when flipping is active #1600

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Merged
merged 1 commit into from
Nov 18, 2023
Merged

Mirror anchor offset when flipping is active #1600

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17 changes: 14 additions & 3 deletions assets/shaders/world2d.vert.glsl
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Original file line number Diff line number Diff line change
Expand Up @@ -40,9 +40,14 @@ void main() {
// this is the position where we want to draw the subtex in 2D
vec4 obj_clip_pos = proj * view * model * vec4(obj_world_position, 1.0);

// if the subtex is flipped, we also need to flip the anchor offset
// essentially, we invert the coordinates for the flipped axis
float anchor_x = float(flip_x) * -1.0 * anchor_offset.x + float(!flip_x) * anchor_offset.x;
float anchor_y = float(flip_y) * -1.0 * anchor_offset.y + float(!flip_y) * anchor_offset.y;

// offset the clip position by the offset of the subtex anchor
// this basically aligns the object position and the subtex anchor
obj_clip_pos += vec4(anchor_offset.xy, 0.0, 0.0);
// imagine this as pinning the subtex to the object position at the subtex anchor point
obj_clip_pos += vec4(anchor_x, anchor_y, 0.0, 0.0);

// create a move matrix for positioning the vertices
// uses the scale and the transformed object position in clip space
Expand All @@ -51,9 +56,15 @@ void main() {
0.0, 0.0, 1.0, 0.0,
obj_clip_pos.x, obj_clip_pos.y, obj_clip_pos.z, 1.0);

// finally calculate the vertex position
// calculate the final vertex position
gl_Position = move * vec4(v_position, 0.0, 1.0);

// if the subtex is flipped, we also need to flip the uv tex coordinates
// essentially, we invert the coordinates for the flipped axis

// !flip_x is default because OpenGL uses bottom-left as its origin
float uv_x = float(!flip_x) * uv.x + float(flip_x) * (1.0 - uv.x);
float uv_y = float(flip_y) * uv.y + float(!flip_y) * (1.0 - uv.y);

vert_uv = vec2(uv_x, uv_y);
}