Function drawLine

src/draw.cpp:1296–1362

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void drawLine( int x1, int y1, int x2, int y2, Uint32 color, Uint8 alpha )
{
    // read color
    Uint8 r, g, b, a;
    getColor(color, &r, &g, &b, &a);
    if (!alpha) {
        return;
    }
    
    // initialize shader if needed, then bind
    if (!lineShader.isInitialized()) {
        static const char v_glsl[] =
            "in vec4 iPosition;"
            "uniform mat4 uProj;"
            "uniform mat4 uMatrix0;"
            "uniform mat4 uMatrix1;"
            "void main() {"
            "if (gl_VertexID == 0) { gl_Position = uProj * uMatrix0 * iPosition; }"
            "else { gl_Position = uProj * uMatrix1 * iPosition; }"
            "}";
        
        static const char f_glsl[] =
            "uniform vec4 uColor;"
            "out vec4 FragColor;"
            "void main() {"
            "FragColor = uColor;"
            "}";
        
        lineShader.init("line shader");
        lineShader.compile(v_glsl, sizeof(v_glsl), Shader::Type::Vertex);
        lineShader.compile(f_glsl, sizeof(f_glsl), Shader::Type::Fragment);
        lineShader.bindAttribLocation("iPosition", 0);
        lineShader.link();
    }
    lineShader.bind();
    GL_CHECK_ERR(glEnable(GL_BLEND));
    
    // upload color
    float cv[] = {r / 255.f, g / 255.f, b / 255.f, alpha / 255.f};
    GL_CHECK_ERR(glUniform4fv(lineShader.uniform("uColor"), 1, cv));
    
    vec4_t v;
    mat4x4 m;
    
    // projection matrix
    mat4x4 proj(1.f);
    (void)ortho(&proj, 0, xres, 0, yres, -1.f, 1.f);
    GL_CHECK_ERR(glUniformMatrix4fv(lineShader.uniform("uProj"), 1, GL_FALSE, (float*)&proj));
    
    // point 1 matrix
    mat4x4 view0(1.f);
    v = {(float)x1, (float)(yres - y1), 0.f, 0.f};
    (void)translate_mat(&m, &view0, &v); view0 = m;
    GL_CHECK_ERR(glUniformMatrix4fv(lineShader.uniform("uMatrix0"), 1, GL_FALSE, (float*)&view0));
    
    // point 2 matrix
    mat4x4 view1(1.f);
    v = {(float)x2, (float)(yres - y2), 0.f, 0.f};