CODEWITHSUNDEEP
c++imageopengltextures
McLovin
McLovin

Reputation: 3417

OpenGL point sprites render as points and not textures

Here's my code

vertex shader

#version 430

in vec3 position;
uniform mat4 MVP;

void main()
{
    gl_Position = MVP * vec4(position, 1.0);
}

fragment shader

#version 430

out vec4 outputColor;
uniform sampler2D tex;

void main()
{
    outputColor = texture(tex, gl_PointCoord);
}

init

void init()
{
    glPointSize(20.0f);
    GLuint tex;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    bmp.Open("C:\\users\\alon\\desktop\\star.bmp");
    bmp.ReadPixels();
    unsigned char *pixels = new unsigned char[bmp.NeededBufferSize()];
    bmp.AssignPixels(pixels);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, bmp.GetWidth(), bmp.GetHeight(), 0, GL_RGB, GL_UNSIGNED_BYTE, pixels);
    delete[] pixels;

    glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
    glEnable(GL_DEPTH_TEST);
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    GLuint VaoId;
    glGenVertexArrays(1, &VaoId);
    glBindVertexArray(VaoId);

    position_index = glGetAttribLocation(program, "position");
    MVP_location = glGetUniformLocation(program, "MVP");

    //                      x      y      z     s     t
    GLfloat vertices[] = {-0.5f, -0.5f, 0.0f,
                           0.5f, -0.5f, 0.0f,
                           0.5f,  0.5f, 0.0f,
                           0.5f,  0.5f, 0.0f,
                          -0.5f,  0.5f, 0.0f,
                          -0.5f, -0.5f, 0.0f};

    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(position_index, 3, GL_FLOAT, GL_FALSE, 0, 0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

render

void render()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnableVertexAttribArray(position_index);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    float c;
    if(bTime)
        c = (float)std::clock() * 2.0f / CLOCKS_PER_SEC;
    else
        c = 0.0f;

    glm::mat4 modelview = glm::rotate(-c * 50.0f, glm::vec3(0.0f, 1.0f, 0.0f));
    modelview = glm::translate(glm::vec3(0.0f + fTranslateX, 0.0f, -1.75f + fTranslateZ)) * modelview;
    glm::mat4 projection = glm::perspective(60.0f, 16.0f/9.0f, 0.10f, 100.0f); //perspective
    glm::mat4 MVP = projection * modelview;

    glUniformMatrix4fv(MVP_location, 1, GL_FALSE, &MVP[0][0]);

    glDrawArrays(GL_POINTS, 0, 6);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glDisableVertexAttribArray(position_index);

    glutSwapBuffers();

    if(glGetError() != GL_NO_ERROR)
        exit(1);
}

The star image is:

  Star image

Output:

  Screenshot

Is there anything I'm doing wrong?

Upvotes: 0

Views: 2143

Answers (1)

Andon M. Coleman
Andon M. Coleman

Reputation: 43329

In compatbility profiles (or any version of GL before 3.1), the behavior you want only occurs when GL_POINT_SPRITE is enabled. In a core profile, that state was removed, and gl_PointCoord always behaves as if GL_POINT_SPRITE were enabled.

To fix your problem, you must call glEnable (GL_POINT_SPRITE).

Upvotes: 2

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