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c++opengl-3

Why do I only see a single color?

I am trying to put either a color or an image to the background of the rectangle I draw using OpenGL 3.3. I'm trying to generate the image color myself for testing, but it seems something is wrong with my code and I only see a single color.

Vertex shader:

#version 330 core
layout(location = 0) in vec2 VertexPosition;
layout(location = 1) in vec2 VertexUV;
out vec2 UV;
void main() {
    gl_Position = vec4(VertexPosition.x, VertexPosition.y, 0.0, 1.0);
    UV = VertexUV;
}

Fragment Shader:

#version 330 core
in vec2 UV;
out vec3 Color;
uniform sampler2D TextureSampler;
void main() {
    Color = texture(TextureSampler, UV).rgb;
}

The way I generate textures:

GLuint data[3] = {64, 128, 192};
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 1, 1, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
glGenerateMipmap(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, 0);

The way I draw my elements:

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex);
glUniform1i(TextureSamplerID, 0);

glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, VertexBuffer);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, nullptr);

glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, UVBuffer);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, nullptr);

glDrawArrays(GL_TRIANGLES, 0, 6);

glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);

glBindTexture(GL_TEXTURE_2D, 0);

The way I generate buffers:

glGenBuffers(1, &VertexBuffer);
glGenBuffers(1, &UVBuffer);

glBindBuffer(GL_ARRAY_BUFFER, VertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

const GLfloat uv_coordinates[] = {
        0.0f, 0.0f,
        1.0f, 0.0f,
        1.0f, 1.0f,

        1.0f, 1.0f,
        0.0f, 1.0f,
        0.0f, 0.0f
};
glBindBuffer(GL_ARRAY_BUFFER, UVBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(uv_coordinates), uv_coordinates, GL_STATIC_DRAW);

When I create and draw a rectangle using these, I see this: enter image description here

I try to generate texture data with these:

GLuint data2[192];
for(int i = 0; i < 192; i++) data2[i] = i;
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 8, 8, 0, GL_RGB, GL_UNSIGNED_BYTE, data2);

and I see this: enter image description here

Solution

  • Since the type which enumerator which is passed to glTexImage2D is GL_UNSIGNED_BYTE, the data typo of the array of pixel data has to be GLubyte (which corresponds to GL_UNSIGNED_BYTE) instead of GLuint:

    GLubyte data2[192];
for(int i = 0; i < 192; i++) data2[i] = i;
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 8, 8, 0, GL_RGB, GL_UNSIGNED_BYTE, data2);