raylib/examples/shaders/resources/shaders/glsl330/ascii.fs

#version 330

// Input from the vertex shader
in vec2 fragTexCoord;

// Output color for the screen
out vec4 finalColor;

uniform sampler2D texture0;
uniform vec2 resolution;

// Fontsize less then 9 may be not complete
uniform float fontSize;

float GreyScale(in vec3 col)
{
    return dot(col, vec3(0.2126, 0.7152, 0.0722));
}

float GetCharacter(int n, vec2 p)
{
	p = floor(p*vec2(-4.0, 4.0) + 2.5);
	
	// Check if the coordinate is inside the 5x5 grid (0 to 4)
	if (clamp(p.x, 0.0, 4.0) == p.x && clamp(p.y, 0.0, 4.0) == p.y)
    {
        int a = int(round(p.x) + 5.0*round(p.y));
        if (((n >> a) & 1) == 1)
        {
            return 1.0;
        }
    }

	return 0.0; // The bit is off, or we are outside the grid
}

// -----------------------------------------------------------------------------
// Main shader logic
// -----------------------------------------------------------------------------

void main() 
{
    vec2 charPixelSize = vec2(fontSize, fontSize);
    vec2 uvCellSize = charPixelSize/resolution;

    // The cell size is based on the fontSize set by application
    vec2 cellUV = floor(fragTexCoord/uvCellSize)*uvCellSize;

    vec3 cellColor = texture(texture0, cellUV).rgb;

    // Gray is used to define what character will be selected to draw
    float gray = GreyScale(cellColor);

	int n =  4096;
    
    // Character set from https://www.shadertoy.com/view/lssGDj
    // Create new bitmaps https://thrill-project.com/archiv/coding/bitmap/
    if (gray > 0.2) n = 65600;    // :
	if (gray > 0.3) n = 18725316; // v
	if (gray > 0.4) n = 15255086; // o 
	if (gray > 0.5) n = 13121101; // &
	if (gray > 0.6) n = 15252014; // 8
	if (gray > 0.7) n = 13195790; // @
	if (gray > 0.8) n = 11512810; // #

    vec2 localUV = (fragTexCoord - cellUV)/uvCellSize; // Range [0.0, 1.0]

    vec2 p = localUV*2.0 - 1.0; // Range [-1.0, 1.0]

    vec3 color = cellColor*GetCharacter(n, p);

    finalColor = vec4(color, 1.0);
}