ghostty/src/shaders/cell.metal
2022-10-31 09:44:37 -07:00

128 lines
3.9 KiB
Metal

using namespace metal;
// The possible modes that a shader can take.
enum Mode : uint8_t {
MODE_BG = 1u,
MODE_FG = 2u,
};
struct Uniforms {
float4x4 projection_matrix;
float2 px_scale;
float2 cell_size;
};
struct VertexIn {
// The mode for this cell.
uint8_t mode [[ attribute(0) ]];
// The grid coordinates (x, y) where x < columns and y < rows
float2 grid_pos [[ attribute(1) ]];
// The color. For BG modes, this is the bg color, for FG modes this is
// the text color. For styles, this is the color of the style.
uchar4 color [[ attribute(5) ]];
// The fields below are present only when rendering text.
// The position of the glyph in the texture (x,y)
uint2 glyph_pos [[ attribute(2) ]];
// The size of the glyph in the texture (w,h)
uint2 glyph_size [[ attribute(3) ]];
// The left and top bearings for the glyph (x,y)
int2 glyph_offset [[ attribute(4) ]];
};
struct VertexOut {
float4 position [[ position ]];
uint8_t mode;
float4 color;
float2 tex_coord;
};
vertex VertexOut uber_vertex(
unsigned int vid [[ vertex_id ]],
VertexIn input [[ stage_in ]],
constant Uniforms &uniforms [[ buffer(1) ]]
) {
// TODO: scale with cell width
float2 cell_size = uniforms.cell_size * uniforms.px_scale;
// Convert the grid x,y into world space x, y by accounting for cell size
float2 cell_pos = cell_size * input.grid_pos;
// Turn the cell position into a vertex point depending on the
// vertex ID. Since we use instanced drawing, we have 4 vertices
// for each corner of the cell. We can use vertex ID to determine
// which one we're looking at. Using this, we can use 1 or 0 to keep
// or discard the value for the vertex.
//
// 0 = top-right
// 1 = bot-right
// 2 = bot-left
// 3 = top-left
float2 position;
position.x = (vid == 0 || vid == 1) ? 1.0f : 0.0f;
position.y = (vid == 0 || vid == 3) ? 0.0f : 1.0f;
VertexOut out;
out.mode = input.mode;
out.color = float4(input.color) / 255.0f;
switch (input.mode) {
case MODE_BG:
// Calculate the final position of our cell in world space.
// We have to add our cell size since our vertices are offset
// one cell up and to the left. (Do the math to verify yourself)
cell_pos = cell_pos + cell_size * position;
out.position = uniforms.projection_matrix * float4(cell_pos.x, cell_pos.y, 0.0f, 1.0f);
break;
case MODE_FG:
float2 glyph_size = float2(input.glyph_size) * uniforms.px_scale;
float2 glyph_offset = float2(input.glyph_offset) * uniforms.px_scale;
// TODO: downsampling
// The glyph_offset.y is the y bearing, a y value that when added
// to the baseline is the offset (+y is up). Our grid goes down.
// So we flip it with `cell_size.y - glyph_offset.y`.
glyph_offset.y = cell_size.y - glyph_offset.y;
// Calculate the final position of the cell which uses our glyph size
// and glyph offset to create the correct bounding box for the glyph.
cell_pos = cell_pos + glyph_size * position + glyph_offset;
out.position = uniforms.projection_matrix * float4(cell_pos.x, cell_pos.y, 0.0f, 1.0f);
// Calculate the texture coordinate in pixels. This is NOT normalized
// (between 0.0 and 1.0) and must be done in the fragment shader.
// TODO: do I need to px_scale?
out.tex_coord = float2(input.glyph_pos) + float2(input.glyph_size) * position;
break;
}
return out;
}
fragment float4 uber_fragment(
VertexOut in [[ stage_in ]],
texture2d<float> textureGreyscale [[ texture(0) ]]
) {
constexpr sampler textureSampler(address::clamp_to_edge, filter::linear);
switch (in.mode) {
case MODE_BG:
return in.color;
case MODE_FG:
// Normalize the texture coordinates to [0,1]
float2 size = float2(textureGreyscale.get_width(), textureGreyscale.get_height());
float2 coord = in.tex_coord / size;
float a = textureGreyscale.sample(textureSampler, coord).r;
return float4(in.color.rgb, in.color.a * a);
}
}