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POWhy is drawing an 8bit texture with OpenGL drawing black pixels instead of transparent?
 

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  1. POWhy is drawing an 8bit texture with OpenGL drawing black pixels instead of transparent?
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    <p><strong>OpenGL Setup:</strong></p> <pre><code>glEnable( GL_BLEND ); glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA ); glEnable( GL_DEPTH_TEST ); glEnable( GL_TEXTURE_2D ); glEnable( GL_CULL_FACE ); glCullFace( GL_BACK ); glClearColor( 0.0, 1.0, 1.0, 1.0 ); </code></pre> <p><strong>Initializing the texture:</strong></p> <pre><code>// 16x16 X pattern uint8_t buffer[ 16*16 ] = { 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, }; GLuint texture_id; glGenTextures( 1, &amp;texture_id ); glBindTexture( GL_TEXTURE_2D, texture_id ); glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA8, 16, 16, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, buffer ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR ); </code></pre> <p>The textures are drawn as quads using glBegin/glEnd. The color for each vertex is white with full alpha: {r=255,g=255,b=255,a=255}.</p> <p>Here's an example scene. The photo and cheese are both loaded from PNG images. The cheese has transparent holes, which show the photo and background behind it. The X pattern I expected to be transparent too:</p> <p><img src="https://i.imgur.com/o1PZH.jpg" alt="Example"></p> <p>Why is the quad black instead of transparent, any how can I fix my code to draw what I was expecting?</p> <p><a href="https://stackoverflow.com/questions/680125/can-i-use-a-grayscale-image-with-the-opengl-glteximage2d-function">This question</a> may be similar, but so far I am unable to apply the brief answer to my current problem.</p> <p>Update: I think I solved it, thanks to the answers below. I changed...</p> <pre><code>glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA8, 16, 16, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, buffer ); </code></pre> <p>to</p> <pre><code>glTexImage2D( GL_TEXTURE_2D, 0, GL_ALPHA, 16, 16, 0, GL_ALPHA, GL_UNSIGNED_BYTE, buffer ); </code></pre> <p>... which gives the desired result.</p>
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