No transparency when using the R8 pixel format

[CaptainKraft]

I'm on Windows using the latest sokol libs.

When rendering an image with the pixel format SG_PIXELFORMAT_R8, and while using a custom shader (shown below), I am unable to render with any transparency.

@vs vs
in vec4 coord;
out vec2 texUV;
void main() {
    gl_Position = vec4(coord.xy, 0.0, 1.0);
    texUV = coord.zw;
}
@end

@fs fs
uniform texture2D iTexChannel0;
uniform sampler iSmpChannel0;
uniform fs_params {
    vec4 iColor;
};
in vec2 texUV;
out vec4 fragColor;
void main() {
    vec4 tex_color = texture(sampler2D(iTexChannel0, iSmpChannel0), texUV) * iColor;
    fragColor = vec4(1, 1, 1, tex_color.r);
}
@end

@program text vs fs

I have the blend mode set correctly, and I'm correctly rendering other images with transparency. When using the above shader, I can even set the fragColor's alpha value to 0, and it will still render fully opaque.

Here is the image description:

    res.img = sg_make_image(&(sg_image_desc){
        .width = res.w,
        .height = res.h,
        .data.subimage[0][0].ptr = temp_bitmap,
        .data.subimage[0][0].size = (size_t)(res.w * res.h),
        .pixel_format = SG_PIXELFORMAT_R8,
    });

When rendering with the default shader, this is what is produced:

And when rendering with the custom shader, this is what is produced:

Am I doing something wrong, or is there a bug in the way that R8 images are being rendered?

[CaptainKraft]

My mistake. I missed the part where I'm supposed to set a blend mode for the pipeline.